I too was very disappointed that this wasn't converted by the author for d20 Modern. I know they wrote most of it before d20 Modern, but damn they had an awful lot of time on their hands before print to change it. And really, they should have. They tried to reinvent the wheel on so many things, and yet could have benefitted from the extensive playtesting that d20 Modern had before going to print, as oppossed to the less-than-extensive playtesting all mini-games get (I believe they have just one team work on playtesting for minis). And I felt it shows. The guns are not balanced against each other, nor against the massive damage rules they proposed (which felt like an afterthought rather than a well-thought-out plan. Like they said to themselves "oh yeah, guns can kill people in one shot, we should put something in there about that!" after the bulk of the rules were already done). And, it seemed as if there were no multi-class rules (though I admit I might have missed it). If that's the case, I feel it detracts significantly from the fun of play.
Overall I am still glad they did this game, but disappointed they didn't take the time to convert it to d20 Modern.