Trouble there is there are a variety of cartridge types even before you get to the more custom stuff with clocks, rumble, infrared communications...
You have two choices (I doubt there are those that put up nice sanded PCBs like in my earlier link, much less for every revision of cartridge* and mbcs in the case of the GB/GBC stuff).
1) You get some working cartridges and try to match things from them. Unlike many times we are dealing in electronics where you either are dealing with some one off part (or near as makes no difference) or you could buy one your chosen online tat merchant but it is going to be food bills/rent for a substantial amount of time to do that there are still cheap GBA games nobody wants (possibly even in the various types mentioned in the * below) at least around here (if you are in Columbia I recognise that is a bit more of a challenge as between repros, Nintendo and other devs not caring then you probably don't have quite the volume of the proverbial Barbie Horse Adventures floating around wherever people sell old junk).
2) The numbers on the top of the chips you are possibly not going to find many datasheets for but you will probably find close enough for most purposes from the same range/company.
http://problemkaputt.de/gbatek.htm#auxgbagamepakbus
https://gbdev.io/pandocs/External_Connectors.html
Should be fairly obvious what connects to what in those cases.
*for the GBA the big three are going to be EEPROM, SRAM and Flash corresponding to the major save types (I imagine no save just uses one of those without the chip). From what I recall seeing one of those has a spot on the board for two different size chips (not quite an unpopulated header but similar principle to save having to design multiple boards). You may also get some differences from when SRAM stopped using battery backed SRAM (most earlier SRAM games) and instead went to FeRAM (still talks like SRAM as far as ROM hackers and coders are concerned but does not need a battery). Pokemon needing a real time clock is another. I don't know if the improved/cheaper ROM chips over the course of the GBA lifetime saw any changes like going from two chips to one but another possibility. What goes for the sub revisions of saves as far as PCB changes I also don't know here but another thing I would consider for generating new revisions of board, though equally how different they might be I don't know.
Bonus the second if you are going to do this is if a PCB is too far gone to fix you might sacrifice said cheap junk game and solder the hopefully still working or fixable chips onto the other PCB instead. I will note however I did see someone selling blank whole GBA boards so it stands to reason cartridges might be an option in this.
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