Having endured financial disappointments in its mortgage servicing business in the latter half of 2002, Matrix Bancorp has found a buyer for its wholesale mortgage banking operation. Matrix, a $1.7 billion company based in Denver, will sell its wholesale mortgage platform to a mortgage banking startup, Ampro Mortgage Corp., through a two-stage process. The company this week sold most of the tangible and intangible property associated with its wholesale business, which generated $3.82 billion