Personally, I’d try to find someone that generally matches my taste (and interests), and this could be done on any dating site. Then, I’d ask them to go for a bike ride with me. I’m sure if you had a boyfriend, he’d be more than happy to do it for you (even with a rented bike). It’s not as if you’re asking him to go shopping or something.
Similarly, I’d like to have a girlfriend who likes board games. But, rather than going on D&D sites looking for female players, I just try to find any girl that is nice, cute, friendly, hopefully intelligent and maybe likes the same music I do. If she happens to enjoy similar hobbies as I do, it would certainly be a perk. If not, I can always still play with my male friends (meaning that in your case, you could still just go on a bike ride alone if your boyfriend turns out to be a total nerd). Just saying.