They may or may not fit other machines, but Felder do a set of 45, 60 and 80mm dia x 110 high sanding drums with a mounting hole of 30mm dia to go on their spindles. The order no. is 09.0.027 - you could check them out on the Felder UK web shop.
I've not used them, but imagine it'd be worth checking even if they fit that the available speeds would suit. I've a feeling that drum sanders usually run at about 1,500rpm, and my Hammer F3 spindle moulder's lowest speed setting is 3,000rpm. I'm not sure how big a deal this extra speed might be, or how much of an issue not having the vertical oscillation of a proper bobbin sander might be.
Felder also do a (rubber?) stick for cleaning sanders (for removing embedded dust from the sandpaper), order no. 10.0.100.
Another option for drum/bobbin sanding is Carroll type bobbins mounted in a pillar drill - i have a set, and they are nicely made. They have a stub shaft that mounts in the chuck. Axminster do them i think, they could be quite a lot cheaper too...
PS added later - just remembered that Carroll also do a 30mm bore sanding drum to suit a spindle. Much cheaper than the Felder items, no idea if this means anything in practical terms.
http://www.clickspeed.co.uk/cgi-bin/eGr ... %20Sanders