There is a company out of Seattle Washington called Acclerator (I am pretty sure their site is acceleratorindustries.com)They make an aluminum catcher for almost any commercial mower. They even have one for some 21's. All of the bags are designed very well and stand up to quite a bit of abuse, the company is very good at taking real world advice to continually improve the design. The biggest plus is that the design allows the mower to keep most of it's vaccuum. Other bags usually will make the mower blow leaves and debris out to the side, this bag doesn't. I have had it almost completely pack full with wet grass, no other bag I have tried will do that.
No I don't own stock in the company, I just feel that they have a great product.
I saw some guys mow a couple of lawns by my summer cabin with a couple of Emarks and those Accelerator bags. They worked great. Really clean cut. Theres a back door that opens and you just dump it all out.
If theres anyway you can order those, go for it. I don't use them but I've seen them used. They work great. I don't think you could go wrong.