I found these two in a charity shop today! I had to sift through two big plastic bins full of old glass marbles (my hands felt absolutely covered in dirt afterwards), but it paid off. Not the best condition, but they were so cheap I had to pick 8 other random marbles just to reach the lowest price given (10 for 5 sek, which is like 50 cents).
ETA: Come to think of it, I've only ever seen Gen 1 marbles before, and they're the only ones I can find when googling it. Where did this Sentret come from?!
I never had any Pokémon marbles as a child, but I have thrifted some before. This is my full collection now:
