Edit: I don't need a replacement anymore
What I did was I got the keycap stem and used a soldering iron with a tip I don't like to kind of weld it back into place. Once I felt it was secure, I coated the edges with super-glue and left it to dry. While this may be kind of fragile, it got the job done and at-least now I can use my numpad 5 key in peace.
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good luck to anyone who reads this post also needing replacement focus alps keycaps...
I got my keycap stem out of the slider by first disassembling the switch (you can open an edge with a finger nail and stick a post-it that's folded twice inside to hold each side open if you don't have an Alps opener), taking out the slider, and sticking in a really thin tweezer in between the edges to push out the slider. It takes a bit of force
good luck