Hi Phil and welcome to the madhouse as you say its a great place for a bit of banter and some excellent advise.
I am not the most experienced pen maker here but I do have fun and have picked up more than a clue.
I know your little lathe quiet well and am sure it has a 1mt shaft thats the taper in the headstock in case you don't know.
My recommended buy for a mandrel would be this: Woodturning Lathe NEW COLLETTED universal Deluxe Pen Mandrel - Planet/Rotur -1mt | eBay.
I have one and use it as and when I feel the need.
I can also recommend Helen as a seller although some of the kits leave something to be desired her service is second to none.
Wishing you bundles of joy young man.
Before i found this wonderful forum i too visited the IAP Home but soon outgrew the brown tongues.
I found YouTube to be one of the best sources of instruction.