You'd have to do some home-made modifications for it to fit.

There is this option though: ]

 

how do i do it though?

 

There's a pin on the stock where it folds. Get a hammer and screw driver and gently knock out the pin. Then using the same pin install the new stock. Depending on the G36 you have the pin can either be knocked down or either up or down. The JG and Echo have pins that can be knocked out either direction

You may want to use a bit of Gorilla glue or something to hold the pin in. Once you take out a G36 pin it tends to fall out easier.

 

is there an adaptor for a scar stock?

 

Not that I know of.

2 Problems I foresee
1. If you attach the SCAR stock on the G36 you'll first notice the stock won't lock into it's open state because of improperly matching mechanisms. And on top of that you can't lock it in the close/folding position.

2. The G36's folding stock hinge is built onto the body of the gun. So even if you have an entire SCAR folding stock you wouldn't be able to do anything with it. You'd have to basically do quite a bit of home-made modifications to get the stock to work.

Those are the reasons I posted the image above of the alternative folding stock for a G36. It's the closest you're gonna get to the SCAR stock without actually using a SCAR stock.
G&P G36 Sniper Folding Stock [GP528] - $95.00 : Airsoft Extreme, The premier American retailer of replica toy airsoft guns.
G&P MK36 KV Stock by: G&P - Airsoft GI - Welcome to the ultimate

 

you'd have to really heavily modify the body to make the scar stock fit, and even then it might not work correctly...