If I remember when I tried, the lower mounts of the trx250r bumper were too close together for the zilla... Zilla has a wider lower frame mount....
I believe I tried a Z400 too and that didnt work... if you give me to the weekend I'll get my trx450r bumper to try but I'm guessing that'll be too narrow as well...
PRM is prob best bet for company that still makes nice bumpers.... armadillo still makes their I believe also... I got lucky and found an AC one for a Zilla on e-bay years ago!