As the title says, where can I buy a sports spring for the front of my '06 1.9 PD L&K estate?

It just failed the mot and searching the net for a replacement doesn't help as I can only find standard/not sports suspension.

Springs should always be replaced in pairs, so you should replace both fronts. For OEM your going to have to pay dealer prices by the looks of it, or fit something aftermarket from Eibach or similar. If you after market you'll need to replace all four.

I had to do this last week. 

Trade Parts Specialists

All other MF's I rang claimed springs were same as std, despite using VIN.

Not cheap, at £77+ but were the correct one according to the paint code

@nickguzzi

Part number I've been quoted is:

1K0411105AT

Can you confirm this is correct part?

I'll have to contact the guy who fitted them.  He showed me the broken one with the colour codes on and also the new one on the car, but its not itemised on the invoice.

He's off racing somewhere.  I've sent a message, will get back when I hear.