This may be a little too old school for you fellas, but I'm in search of a new action slide of a Winchester model 1897 takedown shotgun. Parts for this gun seem rather limited. Any clues on where to look for a new action slide? OR I was thinking about trying to fix it myself with the assistance of a certified welder, my questions is would silver solder be durable enough to try to build up the part that extends back into the action to make it taller? or would it be a better idea to build it up with weld? thanks

First choice is to find a new/used part.

For this, try Gun Parts, Jack First Gun Parts, Poppert's Gun Parts, Bob's Gun Parts.

www.e-gunparts.com/

www.jackfirstgun.com/

www.poppertsgunparts.com/index.htm

www.gun-parts.com/index.html/

If you can't locate a part, heli-arc or Tig welding is the preferred method.  
You really can't "build up" with silver solder, and it's not hard or tough enough to stand up to any use.

I contacted all of those places and no dice, none of them have one. One place even went on to say they get one about once every twenty years or so. Any other suggestions?

A GOOD gunsmith/welder who can build up the part and who knows how to re-fit it.

Is it poping out of the action? If so as has been stated a good smith can fix it.