There's a great reference for radio and microphone pinout diagrams here: www.qsl.net/g4wpw/date.html. That site indicates that the IC-2800H is meant to work with the HM-98 rather than the HM-133, but the pinouts are the same, so if nothing else it will work as a microphone with a PTT button. The fancy buttons on the back are quite different, and who knows if they would work with your radio.
Then there's this site, which says there are actually several versions of the HM-133; the oldest is based on the HM-98. The pictures of the fancy buttons of a couple different versions of the HM-133 look similar, but of course not the same as the HM-98.
I did a web search for "Icom HM-98" and found some for sale for US$ 18.95. That's suspiciously cheap, so it may be a knock-off, but both genuine Icom mics and knockoff Icom mics use electret elements, so a knockoff is likely to sound very similar to a genuine Icom mic anyway. I'd probably buy one of those and try it out. If not you could certainly try an HM-133, but the fancy buttons might not work correctly. Good luck, and let us know what you tried and how it worked in the comments.