What dropshipping companies can complement Printful for bulk orders?

[EssentialTed]

Hey everyone, I recently launched my first Shopify store (dropshipping t-shirts, hoodies, etc.). So far, I am having difficulty getting orders from individuals, but I am surprised by how much interest their seems to be for bulk orders. I am currently using Printful, and from what I have been reading, Printful has a good reputation, but is one of the more highly priced options. I may have an opportunity soon for potentially 400-500 shirts for a fire department. They will want navy blue, 50/50 blend t-shirts. I have having trouble finding this as an option on Printful and have started looking for other dropshipping companies that have what they are looking for. So, I have two questions:

First, can you recommend any dropshipping companies that you have worked with that I should check out?

Second, is there anything I should know about adding an addtional dropshipping source to my Shopify store?

Any advice you can offer would be appreciated.