Hi Jason,
The article on this link gives you a pretty good introduction to the development of the Rootes "forward control van project" and how it developed during its long production run.
http://http://66.129.69.181/forum/topic.asp?TOPIC_ID=182&SearchTerms=commer,history
I'm not claiming that all the info here is 100% correct, but I think it probably will be as close as you can get. Judging by the info in here, yours is a Series II, which ran from 1961 to mid-'63. It has the red Commer badge in the nose.
The Series IIa was not introduced until mid-'63, and the most noticeable difference will be that the red Commer badge between the headlamps was deleted in favour of the now very familiar C O M M E R lettering with individual bold chrome letters.
The PA arrived in September 1965, and did in fact have the double sidelight/indicator setup and new lozenge-shaped grille. The single combined indicator/sidelight - like yours got - died with the Series IIa late summer in 1965.
The PB arrived in 1967 and was pretty similar to the PA.
So there you go
Or not? We all know that export models can differ from the domestic model lineup, so it may not be all that simple after all

Whatever the case, your panel van is fabulous!
For parts, it depends what sort of parts you're after, I suppose. I've just bought exhaust system parts for my 1965 Series IIa from Speedy Spares Services Ltd (near Brighton), and they are shipping the parts to me in Norway today, no problems. Link to their website is found on the main page on this forum. But you could very well speak to our very own Martin Maltas, who runs - among other things - a superb spares service himself. I'm sure he will sell and ship parts to you, and will be an invaluable point of call to all Commer-related issues you may have. His details can also be found on this site, with link to his website.