You could just get them made up at an engineering works, all they are is a set of four bits of aluminium bar 1" long cut off on a lathe, with a hole drilled down the centre of each, plus four allen head bolts 1" longer than stock, use blue locktight to secure the stock nuts onto the bolts and you are done.
This is what I did, cost me $36 Aussie dollars for the complete set