HSU sells 'em, and so do the online audio shops like Parts Express. But I'm not sure how much power you can expect. I know I've seen 100 watt and 250 watt amps, thnigs like that.I have an alternative, one that I'd recommend. Get a good prosound amp, like those made by Crown or QSC. They're made to mount in 19" EIA racks and they're not very large, so you could probably make use of one in the same way as a plate amp. Just attach it to the back of your speaker. That will allow you much more powerful choices.