I heard world wide brands (http://www.worldwidebrands.com/) is a reputable source to find good drop shipping suppliers. Although I've never used it myself, I have read good reviews. Their membership is quite expensive though - $300 for a lifetime subscription!
I suggest that even when you do find a potential supplier, order a small amount from them on your first purchase ($50 or less) just to test out the supplier before fully committing to them. And always have two suppliers just in case one runs out of inventory.
If you want more dropshipping advice, you can check out Shopify's Drop Shipping Guide at http://ecommerce.shopify.com/guides/dropshipping and check out this article http://www.shopify.ca/blog/6492023-drop-shipping-the-easiest-way-to-sell-online#axzz2RKClUHbk. ;
Depending on what type of apparel you are after - check out our website www.ShirtMonkey.co.uk
We sell a range of Tshirts from Funny Tee's to Film Inspired Tee's.
Our catalog is small, but it is growing everyday!
Get in touch and I will offer you a free Drop-Ship account.
We have a shopify store and dropship our products to other businesses
We also offer a 5% mandatory coupon code.
Once you reach 10 sales we will issue you a 10% code and then we raise that again to 15% after further sales.
Our email is email@example.com
Our 5% off code is: 555ROMEO