might wanna check into a paint store like Sherwin Williams, etc. If you tell them what you are doing, might be able to open up a commercial/contractor account, like someone whose profession is painting would do, and you can buy some supplies there.
I get my iso, olfa blades and masking tape when they have good sales.... just a fyi, I also painted the entire exterior of our shop at a discounted price on paint, and picked up stain for my deck this past summer at a good price.