I had similar problems. But a lot of the parts (or similar replacements) are available on aliexpress. Sadly most of them you can’t buy as a single piece, but have to buy in larger quantities. For example the IRM-V538/TR1 is only available as a package of 10 pieces:
… which (obviously) isn’t as cheap as a single one. There may be some electrically compatible IR receivers available too, but not with the same case/construction type.
As a compatible replacement for the DC jack i bought these package of 10 pieces:
They fit perfectly and are cheap as hell. I just hope, they won’t fall apart while soldering 😉 .
The voltage regulator is available too – but (again) only at a larger quantity (5 pcs):
Finding compatible resistors should be no problem at all. You only have to take care that the power-rating, tolerance and (of course) resistance and (last but not least) size are the same. There’s some room in all those values – but i’m no electronics engineer either, so i always try to find the most similar substitute available.
Sadly i couldn’t find a replacement for the two phone jacks needed. I bet, there are some on aliexpress too… but the search function is always kind of a gamble, since weird translations of the description make it hard the find particular things sometimes.