I can?t help with any suppliers of cycloramas.
I know here that cyc?s are not really a hire item as such, but there again we are a pimple on the back side of the world. It may be different there and you may be able to buy a second hand one?
The better cyc?s have a shark tooth weave & the number of tooth stiches per inch will dictate the quality. There are a lot of proprietary brand names such as Robinet & others, but they are all basically a shark tooth weave.
I would imagine the cost of a broadloom cyc would be a few thousand,  made to measure. Although there are a few standard sizes available off the shelve & they can be much cheaper.
Ask your supplier to advise on what it needs to suit your situation, if it flown or dead hung permanently.
If you have Fly?s available & it can be stored in the out position, it may not be necessary to have side stretcher provisions, as this can be done on a gaff basis.
Even if it is dead hung, check the quality of the head eyelet reinforcement band & the even spacing of the eyelets, also that the tail batten pocket will accommodate a pipe batten & is formed evenly & straight.
Once it is in place ensure you educate the cast & crew that the surface of the cloth should not be touched, after it has been hung for sometime, as this will brush off the normal dust, that collects on the weave & it will show up as a mark under lights on the cloth.
A good clue if the cyc is removed & stored, for the handlers to wear cotton gloves, as it can be a drama if a mark is put on it, cleaning can be a major problem, unlike scrims, drops or drapes.
I?m sure the supplier will advise on the care, storage & maintenance of the cloth.

If you think you are going to use the cyc frequently I'd say bite the bullet and buy one.

We needed one a few years ago for a production and decided to just purchase it.  We've used it all the time since then, it has more than made up for the cost.  It was one of those things that you didn't realize how much you needed it until you had it and now you don't know how you lived without it.

We had ours made by Heartland Scenic Studio in Omaha, NE.  We do a lot of business with them, esspecially since they are nearby to us.  Our cyc is similar size to what you need David and it didn't cost all that much.  Of course I couldn't the cost when I checked my file just now but it didn't put a strain on our modest budget.

If you do take the plunge and purchase one you might want to concider a wrap-around.  This cyc makes a right turn stage left and right and heads down stage for a few (5, 10, 15 you decide) feet.  Always nice for those open stage scenes you want in musicals where you want the stage to look like a stage.  Also works well for dance.