Can I get a breast reduction and mammary glands taken out in one surgery?

Yes it's possible to have a mastectomy, just like some transgender patients do, but it's best to discuss this in person, Without an exam, it will not be possible to fully evaluate you and give you recommendations. Be sure to discuss your goals and concerns with your board certified plastic surgeon and consider the pros and the cons. Be certain your surgeon is properly certified.  I've attached a link where you can start your search. 

I believe what you are asking for is a mastectomy or removal of the breasts and this includes all the breast mammary tissue and glands.  Surgically this certainly can be done.  The question is whether this is the best recommendation for you.  Usually this is the plan for trans male patients.  At 18,  I would want to make sure that this is the "right plan" for you psychologically.  You could have a breast reduction without complete removal of the breast and achieve a flatter chest.

What you are asking can be done. Most of the time this is done for transgender patients.  They usually come in with notes from their other doctors supporting the patient's decision.  Best of luck.