Hi Ross, we'll start with the official greeting:
WELCOME TO SEIBERTRON
WARNING SEIBERTRON CONTAINS NUTS!
BEWARE THE PIRATES OF THE ODB!
Next up, where in the world are you? Generally ebay would be your best bet for individual issues of the UK comic, try ebay.co.uk as opposed to ebay.com as they are mostly available from UK rather than US sellers. Be careful with individual issues though, UK news agents in the eighties were in the habit of writing the sirname of people that they were reserving papers or comics for on the covers and this obviously makes them less valuable/desirable. Some specialty comic shops will have a few issues but this probably means more legwork than a straightforward online order.
If you want collected editions Titan Books put out most of the UK material in book form a few years back and these should still be fairly widely available online. Let me know if these collected versions would be acceptable to you and I'll post a list of the titles of the various volumes so you know what you're looking for.