Responses
http://www.mangago.me/read-manga/usagi_to_ookami_no_shinshi_kyoutei/. Not a amusement park, but the two guys do dress in mascot clothes. A wolf and a rabbit. I'll look some more.
http://www.mangago.me/read-manga/xxx_allergy/. I haven't read it yet so not sure... (〜￣△￣)〜
Amusement park job but bear costume. http://www.mangago.me/read-manga/merry_go_round_kubo_sumiko/
i need help finding a yaoi, all i can remember is that its about a couple that has somewhat of a age gap and they work at an amusement park, as well as being the mascots witch i thing is a bunny.