I have a Charles Daly 12 Ga. pump.  It is the "tactical" model. Black nitron finish, extended magazine, synthetic stock.

It is the slickest, best handling 12 ga. I have ever owned. (which covers alot of guns)

Anyways, I wasnt looking for opinions on the weapon but was wondering if any barrels off any other make were interchangable. The shotgun looks similar to an 870.
I would like to have a slug barrel for it but can't find one through "Daly"    

I am not sure if your gun is actually a Zastava "shootgun" http://www.zastava-arms.co.yu/english/civilni.htm , but CD gets a lot of their other guns from them.  CD does not actually make anything, but imports and rebrands guns.  This by no means is a bad thing other than the possibility of them not having parts for them.   Find out who actually made your gun and then go from there if CD customer service is not helping you.