If you can't find a card with the transmit power you want, you may be able to get the range you're looking for from antenna gain and type.
Here is some info if you go the antenna route to improve gain. Note a directional antenna is the best, but then you have to be pointing in the direction... Omnidirectional antennas have less gain because the signal is 360, not focused. For customers needing an off the shelf solution I have ordered 14db and 16db antennas from these two companies and with the proper reverse polarity connector to connect to d-link cards and linksys routers: hyperlinktech in boca raton florida: http://www.hyperlinktech.com/web/antennas_2400_out_directional.php Pacific Wireless in Utah: http://www.pacwireless.com/products/vagi_series.shtml For less than $50 you may can get an antenna and get by with a watt for quite a distance, but you may also need to buy a 'pigtail' (cable with different connectors) to connect. For directional I've had a good gain with the 16db 'VAGI' antenna from Pacific Wireless, and a side benefit is that the average person thinks its a radio antenna and does not realize it is a wifi antenna. BTW, its suppose to have a polarity that changes by rotating 90 degrees, but I could tell no significant difference in signal strength ... In one situation I still had good gain after buying a 50 foot low noise cable with a reverse polarity sma connector to hook to a d-link ap900+ and a type N connector to the soupcan the customer already had. But if you get a long cable you may want to go for the low noise like a LMR 200, or thicker LMR400 ... The down side of the thick cables is that it takes more cable to make a corner (gain drop) and the tension could snap a small connector. In the past I ordered some 'pigtails' from http://www.hdcom.com/pigtails.html or http://www.rfmicrowavecable.com/ good luck !
