I bought the rose joint from an ebay seller:
http://www.ebay.co.uk/itm/180425540596
Name - should the above listing end: 3/8"x3/8" UNF Ultra High Performce Female RH Rose Joint
It's important you get the right hand thread one. I used a 3/8" nut, bolt and washers to connect the pedal. Metric bolts are a smidgen too big.
Seller:
http://www.ebay.co.uk/sch/mcgillmoto...p2047675.l2562