There are quite a places to get your disposable goods. Your roaster is just one possibility. They may buy large wholesale lots and sell at their cost just to give you an incentive to use them as a roaster. This usually only makes sense for you if they are local, otherwise you'll be paying for shipping, which adds up quickly for large boxes of paper goods!
You can also use a Food Service Distributor - sysco, u.s. food service, etc. The catch with these companies is they almost always require a minimum order, but if you are doing food (sandwiches, etc.) also, this may not be a problem and their prices can be competitive. I used u.s. food at my old shop and never had any major problems.
A Wholesale Store is another possibility - Costco, etc. I'm using Costco, out of necessity, right now at a shop I just opened and they have decent prices on paper cups/lids and plastic cups/lids. They don't carry sleeves though.
Many areas have a Local Paper Supply which specializes in a wide range of paper goods, check them out for price comparison.
You probably have a Local Food Service Supply also, Cash and Carry or similar. Check the Yellow Pages and check their prices.
You can also order Online. There a dozens of companies online selling paper cups, etc. I personally wouldn't order this way because I have had way too many problems with online companies. Working with local businesses is my preference for everything, out of belief in local economies (sounds like you are becoming part of this) and for have someone to deal with face-to-face - makes for a better relationship and hopefully fewer hassles. Ordering online often means paying huge shipping charges also.
As far as types of cups, I prefer either Dixie Perfect Touch or Paper Cups with Sleeves. Perfect touch is a nicer cup, made of paper (maybe a touch of plasticized material on the outside?) and doesn't usually require a sleeve. Thin paper with a sleeve is also a good way to go. The cost for the two equals out - thin paper is less expensive but requires a sleeve (as expensive as the cup!) and Perfect Touch cups are more expensive but don't require a sleeve. Definitely sample any cup before you decide to use it. Some types of paper, e.g. some brown cups, flavor the coffee in a strange way.
Stay away from styrofoam! It flavors the drink and fills up the landfill with material that is biodegradable.
There are a lot of newer biodegradable materials out there that I havn't really researched yet.