The yellow HobbyWeld bottles can be refilled by paying for a refill at this page...
Do not put out Argon cylinders! They don't work well with the MIG
There is no HackSpace account, you just pay for it yourself...
HackSpace has agreed to fund one refill per month.
I paid for the last one on 03/09/2015 for September and still need to claim it back, so if somebody wants to order another bottle and charge back through Russ for October that should be fine.
Once you have ordered just leave the empty bottle outside next to the loading bay and the guys will come in and replace it, leaving the new cyclinder and receipt in its place.
They will not give you a delivery time so it may be worth contacting them with the padlock code if you will not be there to receive it.
While I'd prefer not give out the code, considering they are a commercial venture and we have done this a number of times successfully I think its ok in this case.