Seems
demarctech and
zcomax put out cards that do 24.8dbm (302mW) based on Prism 2.5 chipset and they have dual RP-MMCX for external antenna.
The drawback with prism 2.5 under windows at least is no WPA support. With Linux you'll be sweet...
Of course given the USD$160 price tag of these 300mW puppies, one might be better off
getting three 200mW cards for USD$56 each
A