Need advice for custom clothing printing/transfers

Hello, I've had a project going for a while to make custom panties. However finding a method to transfer my designs to panties has been difficult. I was looking into sublimation, and I like the results I have gotten with it (both good quality and price), but finding and ongoing source of solid, light colored undies with at least 60% polyester has proven almost impossible. Not to mention many of my clients are men, and finding men's undies that fit the parameters are even more difficult.

Most of my designs are colorful, so screen print transfers are out of my budget. I've been looking to try some cotton transfers as cotton undies are a lot easier to come by, and I think most cotton transfers can be used on darker fabrics as well as light.

Does anyone have any advice for pointing me in the direction of some good cotton transfers? Or perhaps know of somewhere that I can get a steady supply of nice polyester undies? Or perhaps another method?

I have a small budget currently and I'm trying to do everything myself! I appreciate any help. Thank you!