Hartley and Noble
Click this link to buy through the site with 5% off an order over £80. In return I get a £10 off voucher. I bought the Over-the-Wheel Russian Doll Batt System (No Batt Pins). See Hartley & Noble referral scheme for more info.
The member wheels at the back of Clay Studio are Shimpo Whispa T. For those you want size 300mm.