You can get an 'ancient unix' source license
for $100. It gets you the
source to unix 7th edtion and earlier for personal use. 
I *think* it might also give you rights to use 2.11BSD, the most recent
BSD for pdp-11s, which also comes with source.  Best to contact PUPS
to find out...
                                        Megan Gentry
                                        Former RT-11 Developer
+--------------------------------+-------------------------------------+
| Megan Gentry, EMT/B, PP-ASEL   | Internet (work): 
gentry!zk3.dec.com |
| Unix Support Engineering Group |          (home):  
mbg!world.std.com |
| Compaq Computer Corporation    | addresses need '@' in place of '!'  |
| 110 Spitbrook Rd. ZK03-2/T43   | URL:     
http://world.std.com/~mbg/ |
| Nashua, NH 03062               | "pdp-11 programmer - some assembler |
| (603) 884 1055                 |  required." - mbg                   |
+--------------------------------+-------------------------------------+