Finding vendors shouldn't be too hard with a quick DDG (or Google/Bing/whatever... I'm not naming names because we buy everything new, and the "We buy used xx!!!" spam is summarily filtered out by my personal email filters) search, but fair warning that unless the genset you select is fully integrated (enclosure/genset/belly tank, like the CAT 351x we prefer for our data centers), odds are you'll be buying the generator from one shop, and the enclosure from somewhere else.