I have a triple 50-39-30 and I want to switch to a 44-34-24. (9 speeds)

Sometimes I see chainrings sold as outter chainring or inner chainring (never as the middle one actually), does this really mean anything or I can put whatever chainring anywhere, as long as the BCD and number of speeds is respected ?

I really struggle to find a 34 with a BCD of 130mm, I start thinking it doesn't even exist, if anyone here already has bought one can he please send me the website where he bought it ?

For MTB I guess it would be way easier to find a small triple, but would my sora derailleurs handle MTB triple chainrings ?

Inner chainrings don't have pins/ramps to help shifting up to them. Outer ring should usually be ok as a middle.

38 is the smallest possible 130 chainring, IIRC.

​​​​​​​As for the last bit, I'm not sure how new Sora would do with a newer MTB triple.

Thank you.

Actually if it helps it's a 3400 sora as front derailleur and the rear derailleur would be either sora 3500 or sora r3000 (didn't buy it yet and my current tiagra 4600 needs replacement to have a bigger capacity and to allow more than 27T at the back)

If you just need the low gear, I put a 26T small ring on my 3x9 105 and it works pretty well

Find yourself a 110/74 crank then buy 110/74 chainrings that work with the derailleurs/shifters.

I just reread your post. Sounds like you will be replacing the whole drivetrain. Go to ebay. You should be able to find a good, used higher level 9 speed system for a good price.

Pins and ramps are only needed if your front derailleur is indexed, and only on the middle and outer rings.

They will, but they're also only particularly meaningful in standard configurations. Certain tooth designs can in general have an impact on chain pickup and release (like how Uniglide tends to shift more lightly than earlier designs), but actual shift gates really need correct chainring pairings in order to do their job. My experience with chainring models that have "pins and ramps" without specifying a pairing is that they don't seem to accomplish much.