I had one of the old ones that I believe were distributed with the help of Ann Ball. It was supposed to be wood from his original coffin, it looks like old wood and has a tag on it.
Then, earlier this year, I went to his shrine in Mexico and discovered they offer for a donation relics of wood taken from his reliquary. It doesn’t look the same as the coffin wood and comes in a little box. My understanding is that they have transferred his remains to a new reliquary at least once and possibly twice, so then they cut up these old reliquaries and offer them as relics.
You can also touch your medals and such to his reliquary which is in the Parroquia de la Sagrada Familia, I did that too.
If you’re not going to be in Mexico any time soon to go in person, you could try writing to his museum/ store. It looks like they are trying to put up a Shop website but haven’t quite completed it or at least the shop section is not working for me, but you could try e-mailing them to see if you could get a relic, they had lots when I was there.