Specna Arms SA-A02 Magazines

[Dawnrazor]

Hi,
I was wondering if any of you guys knew where to get 300rnd High Cap mags that fit the Specna Arms SA-A02?
I have one that came with the rifle, but the retailer, Patrolbase.co.uk (and the other ones I've looked at) doesn't sell spares that fit, I've tried the Nuprol ones that work fine in my ASG/ICS Hera Arms CQR and the actual Hera magazine, both are too big, the 300RND mag (with no distinguishing markings, very helpful) that came with my FN F2000 fits fine, but my Nuprol and ICS mags are just too big to fit in the magwell, I have researched and found that the SRC M4 mags fit (and look the same as the one that came with my Specna) and have the same white writing with" 5.56mmx45" and "For Law Enforcement/Government use only" painted on them in white but everywhere I've looked seems to be out of stock and for a mag that would normally cost around £10, if they were in stock they'd be asking £25 a mag!
Does anyone know where I can get mags that will fit and are a reasonable price and still metal externally?
I've read that it is compatible with 
 - BOYI,
 - Airsoft Systems,
 - SRC,
 - King Arms,
 - MAG, 
 - STAR

   and 
 - ACM.
mags but can't seem to find any of them anywhere, I'd like metal High Caps at a reasonable price, but if there's a metal Mid Cap option, I'd be willing to get some of those too for MilSim events.
if anyone knows of any other mags that will fit, or have had the same experience and found other mags that fit (my F2000 could do with a couple more too) I'd be most grateful.

Cheers,

Matt