I would like to repair some minor surface corrosion spots in the rear trunk of my '73 914; once cleaned up and sealed where do I get rattle can paint to match my original paint? Any vendors to order it from?

automotivetouchup.com

Just matched my ford escape and honda accord....availabe in rattle can and other formats...good for small amounts.

Any of your local automotive paint stores will mix one for you. Usually about $50.
NAPA does them also.
The first hard part will be to get the finish to match. Most times the trunks paint is in pretty good shape. Other than the rust area coming from the tail lights.
The second being there's nothing to remove to match the paint too. Usually I remove the gas flap and take it in for a match.
Most of my other vehicles are Ford Oxford white. At last count I think I've seen 9 variants of the one color code.

Good Luck ...........