SINGAPORE (Reuters) - U.S.-based electricity producer Mirant Corp. (NYSE:MIR - News) has begun seeking bids for its multi-billion dollar power plants in the Philippines, sources familiar with the matter said on Wednesday. Mirant has sent out a short sale document on the asset to potential bidders, including some Japanese firms and financial investors, the sources, who asked not to be identified, told Reuters. Mirant is selling its ownership interest in three generating facilities in the Philippines -- in Sual, Pagbilao and Ilijan -- that account for 2,203 MW in generating capacity. Banking sources say the Philippine asset, estimated by some...