Lowes and Home Depot carry small pieces of bare sheet metal. I do not know if they have as heavy as 18ga, but I have bought 20ga there. Also, You can usually pick up a scrap from a local sheet metal shop for a few bucks. I usually try to get a piece of pre primed metal from the sheet metal shop so that it does not rust before I use it and then just sand off the primer when I am ready to paint.
Lowe's and other suppliers got to be just too expensive. I can order 3 times the metal + shipping from cutsmetal .com for what Lowe's wants for 1 sheet.
Another good source for metal sheets on car projects is www.eastwood.com- 18 gauge 24x32 is just $22.00.
Have you got any home heating stores in your area? I get a lot of metal from the store I do installations for, they use the metal to build custom shrouds for fireplace inserts, leftover pieces are usually good size. Dan
Yep...what Dinger said. Look up you local heating and air conditioning company and chances are they will have what you need or probably order it for you. Also if you have any local fabricating shops you may be able to get a piece from them. Depending on what you need to do you can also strip the hood, roof, trunklid off of a junker and use that but would have to strip the paint. There are many resources if you know where to look.
Search ebay for '18ga. cold rolled' You will come up with an outfit in NY caller Frigo Design. I just ordered 1 ton (yes that's right 2000#) shipped to my door for $421.00 They normally sell it in lots of 1500#, but for a small fee, they will up it to an even ton.
Great stuff if you like 18 ga. I normally use 19ga for automotive panels, but the 18ga will work fine too.
Ferguson Coachbuilding www.metalmeet.com
NEW '37-'42 Willys replacement panels now available!
Another great place (if you have one in your area) is a steel salvage yard. The one in my area has anything and everything you can think of from round to square and paper thin to as much as an inch or more thick. The last time I was there I loaded what must have been all of 300 lbs. of steel on my car trailer for $20.00. I found 1/4 in. steel approx. 8" wide by 15' long and used them for boxing my frame.
My local NAPA, which is a pretty big one, carries sheet metal for body work. I'm not sure how their price compares to all the other suggestions-I would guess less than Lowe's and more than a sheet metal suppliers. You might also check out some older hardware stores.If they had the stuff,they might have the old prices on it,too.