Harbor Freight has an E-torx assortment.
I've got a couple of sets- but I'm not sure how big they go.......
EDIT:
here's one of the sets I have (looks like it only goes to E16):
http://www.lislecorp.com/tool_detail.cfm?detail=370
It does say that E18 + E20 sockets are available from Lisle separately...
I think I got my set at Autozone or Pep Boys, but that was many years ago. I'd make the rounds of the discount auto parts places, one of them is bound to have something.
OR, you might want to try to find this "Master" set:
http://www.lislecorp.com/tool_detail.cfm?detail=339
$32.95 MSRP
EDIT #2- if you strike out completely, you might want to check out the Raleigh Flea Market- there's a tool guy there every weekend, in a big tent outside. He's got alot of the HF-type stuff, and he *might* have what you need.