I found one on eBay with 1700 mAh are there bigger ones??
http://cgi.ebay.de/Power-Akku-f-HTC-Touch-HD-Pro-HD-Blackstone-1700mAh_W0QQitemZ390061743029QQcmdZViewItemQQptZDE_PDA_Zubehör_KM?hash=item5ad17ddbb5&_trksid=p4634.c0.m14.l1262&_trkparms=%7C301%3A1%7C293%3A2%7C294%3A30
http://cgi.ebay.de/Power-Akku-f-HTC-Touch-HD-Pro-HD-Blackstone-1700mAh_W0QQitemZ390061743029QQcmdZViewItemQQptZDE_PDA_Zubehör_KM?hash=item5ad17ddbb5&_trksid=p4634.c0.m14.l1262&_trkparms=%7C301%3A1%7C293%3A2%7C294%3A30