Unfortunately I can't find a naniwa 3/8 anywhere in the UK. Certainly not for a cheaper price. If anyone has found anywhere in the UK that sells one I'd be keen to know.
In the meantime, I guess my plan will be to get a Norton 4k/8k and a leather strop for complete self sufficiency.
Japanese Waterstones: Naniwa Super Stones
It's not in UK, but shipping should be in the order of 10 euro.
If you are looking for natural finishing hones aj_1001 on eBay is a seller of Welsh hones, he's in the UK so shipping to the UK should be very reasonable . If you search on Ebay for barber hones, Swaty (three line) and Apart hones are considered very good. A CrOx pasted paddle is also a great option for refreshing an edge. If you need more, as others have said the Norton 4/8 or the King 3/8 should be fine. You won't need more unless you need to fix real damage.
I have used only a barber's hone to maintain my razors for the last 3 years. You can get caught up in the hype of buying many hones,but unless you see yourself buying abused razors that need restoring,it really isn't necessary.The trick is to do preventive maintenance. Give it a few laps every few shaves,and don't wait until it starts tugging and pulling.