According to Jack :
I have to move my stove to the other side of my kitchen for a couple of
weeks due to construcion. It is electric, and from what I can tell,
220v extension cords don't exist. .

You make them.

For longer term use, you'd buy something like 4 wire Sxxx or SJxx cord
(stranded flexible heavy or medium duty), and buy the appropriate plug to
match the existing socket. Often, you buy and install a matching
socket into a box for the other end of the cord.

These things ain't cheap tho. The plug runs around $15, and depending
on a variety of things, you could end up paying more than that for the
socket. 4 wire #6 Sxxx cord could run over $3/foot. I spent almost
$50 making up a 15' 240V (3 wire) 40A extension. You might have to
spend about twice that.

I plan to disconnect the 220v wall plug, wire in a 20 foot jumper
section of #6 cable, then re-attach wall plug to end up jumper. Will
run temporary wire under kitchen floor/on basement ceiling.

My questions is this, are there #6 wire nuts, or so you use a different
technique to connect #6 wire?

As others have mentioned, there are suitable wirenuts. The package
should list exactly what combinations of wire are permitted.

A 20' length of #6/3 is going to be a lot cheaper than making up a 20'
"extension cord". As long as the #6/3 can't get kicked out of the wall
(which it sounds as if it can't), and you have a reasonable grounded
and protected socket at the stove end, this works fine, and inspectors
won't bitch.

--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.