Hi Colin, welcome along to the site. As you say, it can be very good for your mental welfare turning pens (well, until a blank is just about finished and then decides to split! 
)
I have used a company near you for pen blanks, (to suppliment the off-cuts I get from other sources for free), they are https://www.woodwiseuk.co.uk/product-category/pen-blanks-knife-blank/pen-blanks/ Their service is very good and they have quite a range in stock, I'd advise some of the cheaper blanks at first, but occasionally I get a few of the more expensive blanks as well, just as a little treat for myself 
Also, if you don't mind a little travelling, I have the good fortune in my day to day job of truck driving to visit https://www.sykestimber.co.uk/ They have an off-cuts shed which I like to have a rake around in when I'm loading from their premises. (Did I say 'good fortune', my wallet doesn't seem to think so as I always end up coming out with more off-cuts than I need, but hey we need a little treat once in a while 
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Hope this helps, and you enjoy your time at the lathe.
P.S. as for pen kits, I would recommend https://www.cscrafts.co.uk/ I use them for most of my kits, they are local to me and I can't fault their service.
