There's nothing "special" about your door key . . . it should use the same blank that all 71-79 type 1 and type 3's used, but you probably won't find many hardware stores that stock them anymore.  I think I got the last ones Ace here in LaFayette had about 15 years ago.  I got tired of not being able to find the blanks, and when I did, finding someone that could actually copy one correctly, so I took a locksmith course, got a VW code book and a key machine . . . and eventually bought the contents of an old locksmith shop.  I've the blanks you need.  And if I ever get Homer cleaned out, I might actually be able to get to them.