Yes I've got The Sacred Language of the Sikhs - it was suprisingly easy to get and really cheap - I think I was in the right place at the right time. I got it from alibris.com.
I can get A Guru Nanak Glossary from a local bookseller for, wait for it, $350 AUD!!!
I've seen a couple on Amazon for ~$50 but it's saying it won't ship to Oz. I've messaged one of the sellers to find out if they can make an exception.
Other than that the $100 from Barnes and Nobel is looking pretty good.
But since it is so pricey and tricky to get, I don't want to go to the effort if it's not very good. I think it will be pretty good though. Shackle seems to know what he's talking about, but you've still got to be careful of low-flying Christianisms.