Short answer: Generous neighbour(s)
As a very young child, I used to race to the door on certain days of the week to grab "The Beezer" before my brother and "Misty" before my sister. Some years later, we had a new neighbour whose husband and sons had amassed too many comics for their loft to hold and so she would give us piles of their older comics (including Spiderman nos. 1+, Hulk nos 1+, Doc Strange, Rampage, Mad and Frantic) in order to clear space for more meaningful loft clutter. I loved these comics - they made the Beezer and Misty seem so tame and childish.
My brother started to buy DC comics with his Saturday job money and, of course, I would sneak a read of these. However, I preferred the Marvel cast-offs as I found the DC superheroes to be far too squeaky clean and shiny. Then our kindly neighbour from heaven handed me (because I always said "thank you") a great pile of 2000ADs: issue 1 through to about 100. All in pristine condition. My brother, by that time, had discovered girls and had only a passing interest in this strange comic with its green host: Tharg. I, on the other hand, became hooked. I even got myself a weekend waitressing job (for which I lied about my age) so I could buy the current issues.
I remember developing a fantasy crush on the tusked chappie in the Halo Jones series (I was already weird: Captain Scarlett used to rock my young boat too!) I also remember the day that 2000AD went full colour as I hated the change and stopped buying it for a while. To fill the void, I started to read and collect a new comic called Hellblazer. And in later years at uni, because I didn't know better - having no role model other than the kindly neighbour from heaven - I gave all of my early Hellblazers to a guy I used to hang out with. (Doh! Doh! Doh!)
Oh...and the pristine set of 2000AD's and early Marvel issues? As soon as I had left home to attend college, Mum redecorated my bedroom and placed all of my comics in boxes in the garden shed. Mice, damp and mould killed off any possibility of early retirement from the sale of first editions. I didn't appreciate the enormity of these losses until shopping for replacement back issues in my early thirties.