Im not sure how it's done elsewhere but in Japan spare parts business is a lucrative venture. Those ambitious enough do it by themselves. Depending on your approach plans and parts interested with , a 40ft container can be done within 1 -3 months. Main source is accidental or disposal cars which are very cheap or free sometimes.
The major challenge is dismantling yard as they must have a special permit from government.
@rahatupu 5 cars is economically not advisable. You need at least 20ft container.
work to prosper