looking to get a whetstone for sharpening kitchen knives
can't seem to find them in local cookshops so going to buy online
they seem to vary in price quite a bit and I'm not sure what coarseness I need.

can anyone tell me what grade I need to sharpen kitchen knives and any good online sites for buying?

Not sure, but I've got an ancient 'oilstone' which was my granddads, It seems really fine & I can get a good edge on me Victorinox army knife.
The other stone I have has a 'rough' & a 'medium' side to it but I only use that for my fishing knife (bait cutting, not filleting)

Check out http://www.britishblades.com and http://www.bushcraftuk.com. I found tons of posts and advice about knife sharpening when I was looking. There's some pretty knowledgeable fellas on them both.

http://www.bushcraftuk.com/forum/showthread.php?t=12348
http://www.bushcraftuk.com/forum/showthread.php?t=11571

A couple of useful tutorials

What type of knives have you got?

David Mellor carving, cooks and chopping knives and an Anolon Santoku
all carbon steel