Unfortunately, these things change a lot. And my time out of the industry will make answers speculative at best. I can tell you that being a low volume seller is HARD. And for good reasons on the part of both the publishers AND the distributors.
On the part of publishers, they do not want the distributors to sell such low volumes that they essentially become a discount retailer undercutting other retailers. If anyone out there could set up an account and buy, then that is what will happen. As a result, to buy from a distributor, you typically need to hit minimum order sizes (and those change so I am reluctant to give you dollar numbers) AND have tax information indicating you are a business. That required information changes from state to state. You may already have that if you are a publisher.
On the part of the distributors, they don't get much value out of low volume buyers. They would rather have one BIG customer than have ten smaller customers. (Obviously, they would prefer to have ALL the customers.) At a certain point, they lose their profit margin if the volume gets too low. It's just not what they are set up to do. Also remember that they are getting paid much less than cover price (so that the retailer can see for cover price) so it's not like they can be Amazon.
Anyway, we used Diamond for comics (you gotta use Diamond if you are gonna sell comics). And we used Alliance for games. There were always a few companies we would buy direct from but that is kind of a pain. I'm sure you've run into this trying to sell direct to retailers (thus your desire to sell to a distributor).
I never sold anything to a distributor so I cannot give you any advice there other than to say that Alliance was the biggest. I don't know if that's still the case.
Anyway, I hope that was helpful and good luck!