I had to try a lot of hays to find one my girls liked ><
ANY "horse quality" (as opposed to cow quality, which can have nasty stuff like mildew in it) grass hay is suitable for rabbits, though with "cereal" types like oat, wheat, rye, etc. the seed heads (oats or w/e) need to be removed before feeding it as all those extra carbs and calories are no good for bunnies and can cause serious health problems.
I recommend calling around to local feed stores to find out what kind(s) of grass hay they sell (you need to specify grass, as horses are often also fed a legume hay like alfalfa/lucerne; feed store employees should know which of their hays are grass and which are legume hays). Explain that you have a very picky rabbit and politely ask if they would let you get a small handful of their hay (or each type if they sell more than one kind of grass hay) for your bunny to taste-test before you commit to buying an entire bale that your rabbit may not even want to eat - many places will say yes (as no one's going to notice one little handful missing from a huge bale of hay
).
Feed store (ie any place that sells livestock supplies) hay is typically fresher and better than pet store hay... and it's a fraction of the cost. I did the math, based on US pet store prices and average feed store prices - assuming you buy the largest/best price pet store bags (around $3 a lb), you'd save around $3,000 in a bunny's lifetime (assuming a medium sized rabbit and average lifespan of 10 years) by buying feed store hay instead. A bale can be stored for a year or more if kept clean, dry and insect free. Heck, even if you don't have room for a whole bale, you'll still save a ridiculous amount of money if you pay for a whole bale but only take home half!
If you don't have the means to transport and store a whole bale (or half of one) or can't find feed stores, another option is to call around to stables in your area - any place that boards horses, offers horseback riding lessons, sells trail rides, etc. (basically, a business that has horses on the premises). Explain that you're in need of grass hay for your rabbit and ask if they'd be willing to sell you a few flakes (flakes are what bales are broken down into). A lot of places will, and some will even tell you that you can have a couple flakes for free.