A GREAT place you might want to try is Yalaha Bakery located at 8210 County Road 48 in Yalaha, FL 34797. It's just outside of Orlando in a very rural area, but SO worth the drive!
The bakery has lots of German-style pastries, and their deli stocks various German meats, sausages, etc. In fact, they'll make up custom sandwiches for you, as well as salads, that you can eat inside or outside.
The line of customers can get pretty long for the bakery side of the building, but the deli / restaurant side isn't too bad.
Get there early for the best selection. Hope this helps!!!
You may want to try the International Market & Deli at 815 N. Mills Avenue, just north of Colonial Drive (a major intersection near downtown Orlando). Their phone number is 407-228-2821. They specialize more in Russian, Polish, and other Eastern European meats and groceries, but they might have some of those things (or know where to find them).
Beyond that, Hollerbach's Willow Tree Cafe in Sanford is known as the best German restaurant in Central Florida, and they definitely have knockwurst and other wursts:
Hollerbach's Willow Tree Cafe
205 E 1st St Ste D, Sanford, FL 32771