Try e-gunparts.com, gun shows, gun shops, custom stock makers.
Herters was the importer, not the maker- and has been out of business since the 1970s. I believe those rifles were made in Yugoslavia, and used a Yugo Mauser action. A gunsmith MAY be able to fit a commercial Mauser stock to your rifle, but I know of no ready source of parts for these. Sorry-
No, the Remington Model 1100 stock has a hole (recepticle) through the inside of the stock in the pistol grip area to accept the action spring tube. The Remington Model 870 stock has no need for this hole so the 870 stock will not fit on the Model 1100 action.
Not without modifications
100-400 or so.
It was built with a commercial 98 Mauser action.
Yes it is
Yes, the Deluxe Model
700 ADL Long Action
You must provide the name of the maker, type of action and caliber/gauge.
Not easily or readily.
Based on cartridge size, 30-06 and longer is a long action. .308 and shorter is short action.
$1000-1500 depending on the condition of the stock blueing and action.