Don't think Mountney, or anyone else for that matter, do one any more. Don't panic tho', just read the posts from myself & Nige on page 1 of this thread
As for the SE / S2 thing depends on how you get your S2 'Nardi' wheel as these are supplied with a seperate boss, see section 32.05 of your parts guide. If second hand you would probably get it complete with boss etc.
However if you follow Nige's instructions for the SE wheel you will uncover a 'boss'. This has Nardi stamped on it which leads me to believe that both SE & S2 'Nardi' wheels are in fact both made by Nardi!
You can then use this boss, together with a suitable adapter & shroud, to bolt on whatever wheel you fancy
