If you can't get STP60s then try to get their equivalents, for example: IRFZ48, IRFP048, SUP75, BUK7508, and so on ..
Try RS Components Malaysia: www.rsmalaysia.com
For your info, I already tried to change STP60NF06 to STP60N06, but the UPS (Unintteruptible Power Supply) is not working. Their is not output voltage in the output point.