Any one know of online mag suppliers that can help.
New and older out of production guns.

I found used mags for my a S&W 5943 at Numrich Gun Parts.  They were all 15 rounders, though.  They do have new and used mags for all sorts of firearms.

https://www.gunpartscorp.com/

If you have specific firearms in mind, it might help to share what they are.  Arfcom members love a good challenge in finding things on the internet.

Why?

Cant speak for OP but some folks fully believe a 10 rd mag ban is going to be passed and signed.   They dont want to be in violation and get low cap mags while they can.

As for original question, I agree best results will be in asking for specific models.   Unless maybe if you find a retailer/seller in a state that already has an existing ban.

@LILGUY did you get the answer(s) you needed?  Lots of people in here who would be willing to help you out if you had more specific questions.

https://www.magazineblocks.com/magento/products/magblock-kits.html?mode=list

This for conversion.

https://www.mec-gar.com

New OEM comparable.

So far.

Weren't you the guy that posted on Illinoiscarry that you were going to start selling all of your firearms after jelly doughnut got elected??

Correct, marched into Cabelas before his inauguration and got 60 cents on the dollar for nine units. I have the receipt if anyone comes asking. Several carry guns I want to be ahead of the game if and when they change the law.
With all that being said, I’m still very much in the game. I’m a NRA basic pistol instructor and RSO at my gun club. Every quarter now  I send 100 dollar checks to four groups.
NRA
ISRA
SAF
IC
That’s a minimum 1600.00 a year now on a retired auto techs earnings. I know we’re in the fight of our lives.I’ve had my FOID since 1972  and became a NRA lifer over 40 years ago because I was incensed by Illinois’ licensing system. Now I’m doing it for my kids and grand kids so hopefully they will still be able to exercise their 2nd Amendment right long after I’m gone. Question answered?

The question was primarily rhetorical.  Ten-round mags for most weapons can be found on the net with a little searching.  However, standard capacity mags are likely the only choice for older weapons so you might as well give those away too.

Wonder where I can find 7 round magazines for a Glock 17.