Is this for a Cat or a Raft? Most of the vendors listed above are speed rail fitting builders. If you are looking for the highest quality welded frame, you won't find a nicer one for fit and finish and design than canyon whitewater inflatables and the prices are near what you would pay for a handrail boat.
I have heard they can also beat most of the pricing on speed rail fitting boats but don't do them often.
I have bought stuff from Ron at riverboat works also , good service.