You can try getting a replacement plastic or aluminum top radiator, this is usually made in Taiwan, Thailand or other S.E. Asia countries. They are much cheaper than copper-brass radiators. Another option is using second hand radiators (surplus in the local lingo) but you may again encounter the similar issues you're having.

Try scouting at any auto supply shop near you. Places like Banawe st. in Quezon City, Evangelista st. in Makati, and LRT EDSA Taft in Pasay City have quite a large selection of auto supply shops and you can also haggle a bit.

Last year I was quoted a Nissan Pathfinder radiator for Php2000, this was in Banawe