Where can i find a motherboard and processor for a dell inspiron 1505

You will need to order the motherboard from Dell. The CPU can be ordered from anywhere as long as it is the same as the one you already have.
 
Ebay is really the best way to go if you want to replace those parts. It would probably be best to get a used/refurb newer laptop. (or a new lower performance laptop after all the $$ and time spent to replace your old parts.)

A newer, base line laptop would probably be better than the one you have now anyways...