If you ship a gun into the UK, it is always more or less going to get spotted by customs. I wouldn't class that as two-tone as it's not two-tone enough.
There are loads of great websites which can give you a quality gun and will two-tone it for you. Take a look at proairsoftsupplies, zeroone. Anything without "just" or "bbguns" in the name.
If you're at starting airsoft, take a look at G&G rifles, I vouch for them and I'm pretty sure that everyone else on this forum will as well.