Can you get 800cc silicone implants to replace 1st breast aug? My 600cc seem small.

Appropriate breast implant size is determined by a patient's breast measurements, skin quality, and overall body shape. In your case, an in-person consultation with a plastic surgeon would be best. 

Breast implant selection is best done in the setting of a formal consultation with a board certified plastic surgeon.

Choose your surgeon carefully; this is the most important decision you will make in regards to your breast augmentation. All members of the American Society for Aesthetic Plastic Surgery are board certified in plastic surgery with experience in cosmetic surgery. surgery.org will give you a list of such surgeons in your area.

Come to your consultation prepared to discuss your aesthetic goals - bust fullness, figure balance and breast shape. Bringing photos to illustrate your point can be helpful. After an examination your surgeon will be able to discuss and recommend particular implants that will best achieve your aesthetic goals. Some surgeons will use various tools to help patients choose their implants. Implant sizing, 2D photography, 3D photography and photo gallery review are a few. Ultimately I believe the patient should make the final decision with regards to the implant. I believe the surgeon's role is to offer advice; I do not think the surgeon's role is to dictate which implants patients choose.

600 cc implants are quite large and 800 are as big as they get.  Without seeing you in person, it is difficult to say whether or not this is reasonable for you.

Thank you for the question. 
In regards to specific size/profile of breast implant, despite good intentions, online consultants will not be able to provide you with  meaningful specific advice.  Ultimately, in person consultation with well experienced board-certified plastic surgeons will be necessary. Careful measurements, dimensional planning, and careful communication will be key.
Generally speaking, the best online advice I can give to ladies who are considering revisionary breast augmentation surgery (regarding breast implant size/profile selection) is:
1. Concentrate on choosing your plastic surgeon carefully.  Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you're looking for. Ask to see lots of examples of his/her work.  
2.  Again, have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining which operation and/or breast implant size/type/profile will most likely help achieve your goals.
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or "C or D cup" or "fake look" etc means different things to different people and therefore prove unhelpful.
 Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup  size may also be inaccurate.   3.  Once you feel you have communicated your goals clearly,  allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals.  Again, in my practice, this decision is usually made during surgery.  The use of temporary intraoperative sizers with the patient in the upright position makes selection of the best breast implant size/profile relatively easy.
I hope this, and the attached link (dedicated to larger breast augmentation outcomes,  with many examples of patients with 800 cc or greater volume), helps.

800 cc implants are the largest available on the market
today, and aren’t used as often in cosmetic breast augmentation as they are
with reconstructive surgery following a mastectomy. Choosing implants that
large isn’t impossible, but does require some specific physical requirements.
First, the breast diameter must be wide enough to support implants that large.
Additionally, existing skin and breast tissue need to have sufficient
elasticity to accommodate the implants. Also, depending on how long you’ve had
your implants, you should wait at least six months after your breast
augmentation before pursuing revision surgery. Implants that seem small at
first may settle and “fluff” over the next few months as your body adjusts.

800 cc breast implants are extremely large and typically only used for breast reconstruction after mastectomy.Whether your breast can accommodate 800 cc breast implants will depend on your current breast and chest size.  If you have had 600 cc breast implants most likely your breasts have been stretched to the point where you might be able to accept the additional volume.However I urge you to consider this step carefully.  Please consult a board certified plastic surgeon.For more information on breast implant revision please read the following link: