parts stores
We used to sell it by the case if requested at the auto parts / body supply places I worked at...but it would probably be cheaper at a Wal-Mart or other big box store..we gave a 10% discount on anything bought by the case,but the parts stores cant buy or resell it as cheap as the bigger stores...personally,I'd buy a quart of gloss black Rustoleum or similar enamel and a cheap spray gun-

..one "bargain outlet" type store nearby sells touch up and regular spray guns for less than 20 bucks--China made,but good enough for a paint job or two...better off for primer coats than finish work though,unless your not too fussy about a smooth finish...they work pretty good for the price...
-I've seen those Wagner "Power Painter" electric "buzz box" sprayers do a decent job on frames and underhood jobs where a showroom finish is not required..they also sell "Pre-Val" sprayers and similar units you can pour the paint in and pressurize it with disposable cartidges-,
,or pump up with a compressor...paint in liquid form goes further,lasts longer,and prevents rust longer than spray paint in most cases...much cheaper too!--a quart will probably do ALL the underhood areas for about 6-10 bucks(Rustoleum)--or at least 3-4 cans of spray paint at 3-5 bucks each..

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