I just came across this, looks like the 1000 rounder which comes with the budget Thompson but it`s available separately for a tenner. I believe the spine on the back of the mag needs sanding slightly to fit a normal tommy aeg, there was a thread on here about it but can`t find it at the moment.
http://www.justbbguns.co.uk/product/70/Magazines/149/Rifle-Magazines/718/THOMPSON-DRUM-MAG
£20 delivery to the isle of man!!! 
I have an old airsoft Thompson drum mag in a pouch that has outlived almost 2 thompsons until I found it the other day!
Quite frankly, the Cyma one is better for one major reason:
The loading opening is to one side. This means to refill the Cyma drum mag, you don't have to remove it from the gun.
Restricted time for reload.
Apart from not having to remove the magazine, you can pour 400-odd in in one go, no speedloader required, you can wind it easily, and if you get caught while doing it, your gun will fire...
I ordered one of these and paid on 29th March. £10.00 plus £3.00 delivery..
I thought it was a while coming, and now I receive a paypal notification a partial refund of £10.00?
I have just phoned them to find out what is going on, they said the refund was because they are out of stock of the drum mags and sorry they don't know why you didn't get the full refund and they will refund the extra £3.00 immediately.. I replied I just want the mag and that it was showing in stock when I paid for it, they then said they don't know how that happened or when they will be getting them back in stock, if ever.. I then ask why are you still showing them on your web site, and the honest reply came back, "to generate interest"..
I thought the deal looked to good to be true!
'Non adepto demens. Adepto etiam'
War does not show who is right, only who is left..
