I think I found out the solution, although not as cheap as I'd like:
- Buy 3 of these, so 9 x 100w lightbulb:
http://www.ebay.co.uk/itm/X3-100W-ES-PEARL-48V-50V-GLS-LAMP-LIGHT-BULB-LOW-VOLTAGE-/140874761935?pt=UK_Light_Bulbs&hash=item20ccca46cf
- And these holder...