Affiliate Marketing Secrets

I am participating in a fundraiser to raise awareness about pregnancy health and we wanted to sell maternity t-shirts with our logo/message on them at some events. I have been looking for a wholesaler where I can buy the maternity shirts either blank or even pre-printed & this specialty niche clothing item seems to be VERY pricey compared to regular shirts from the little info I have found on it! Can anyone point me in the right direction as to where I can look for wholesale/bulk maternity clothes? Thank you!