You could lay up your own. And it's likely that you could tune the Bimini
so that they don't have to be round. Which would give you a lot more latitude in terms of what you use, buy, or build, in terms of "rods". Much of it will depend on what they're meant to connect with on their ends, & also, how much stiffness or flexibility you need.
You might also look at:
- FRP Stock, Battens, or Sheet. Or even Aluminum
, or other metal battens/stock.
- Sail battens: Wood, Fiberglass
, Carbon Fiber, etc. Or any combination of these materials. Be they store bought, or DIY.
- Pipe/Tubing. Be it Aluminum
, Fiberglass, PVC, or Other.
- Bamboo, & similar natural, pre-made structures/structural bits.
So the options are limited mostly by imagination, more than $. And there are likely to be dozens of choices on sight (locally), cheap
. Just look for the equivalent strength & stiffness in non-marine shopping
locations in order to keep the price
Hope that helps.
Edit: Even bundles of small diameter tubes siezed together at intervals would work. As they form a macro equivalent of laminated parallel glass fibers. And wood is mostly just a bunch of micro diameter tubes bundled together in parallel in it's natural form.
Remember the bow Arnold made this way from siezed together bundled reeds in Predator