My breasts are different sizes. Will insurance cover costs for beast implants?

The concrete answer is not usually, but in some instances it might be possible. The best way to find out is to have a consultation with a board certified plastic surgeon. Your insurance may require you to have your PCP submit a referral. 

Your description of your situation suggests a possible chest wall or developmental deformity of the breasts.  If this is the case, many insurers will cover "reconstructive surgery" to correct the underlying problems.  However, if the issue is primarily cosmetic, insurance may not cover or may only partially cover the breast surgery.  As there is no way to absolutely predict this coverage, you should seek a consultation with a Board Certified Plastic Surgeon who can evaluate your condition and make appropriate recommendations.  If your surgeon feels this is a reconstructive surgery, then pre-authorizing/pre-certifying the surgery with your insurance carrier will be necessary.  This is the process that all of your information including office records, photographs, supporting documentation from other health providers is submitted along with the planned surgical procedure codes to your insurance carrier.  They will render an opinion as to the liklihood of coverage.  Nothing is guaranteed until the actual surgery is performed and the codes/documentation is provided to the insurance carrier.Best to get help from your preferred Plastic Surgeon and his office staff.  You can also inquire directly from your insurance carrier as to the types of procedures covered under your plan.

Insurers rarely cover implants except for reconstruction after cancer surgery. They might cover reduction of the larger breast if you have appropriately documented symptoms that might be caused by breast size. The amount of breast tissue that would have to be removed may be more than you would want removed, however. Although there are no photos posted, I would expect a more complex than average decision process, and operation, with higher than average risk of needing a touch up procedure.  In that setting you may want to think about whether you really want to travel out of town for surgery. Your breasts will be much more even after surgery, but will not be identical (none are). Pregnancy changes are not predictable, but it is likely that you will have differential breast changes and recovery from the pregnancy and nursing. In person consultations will be much more helpful than on line advice!  All the best.