I've come across a button maker and 500 "blanks". I want to say that this is what they looked like when we redid the upholstery in our 1973 Charger, but am not sure(was 7-8years ago). I wouldn't have thought of it possibly being useful when I first saw it, but a couple were sitting in the box in blue and it made me remember the Chargers seats. I'm sure most people just reuse the ones you took off, but maybe not. I don't see anything on Legendary's website. There is an actual press that was in another part of the garage at the estate sale but I didn't think anything of it. Now I see the instructions showing it, which would make this a lot easier to make them. The lady said they might have another auction and they still had a lot of stuff people didn't want and left there. Hopefully that press is one of them so I can get it.
I'll upload a picture on my phone in a second. The buttons is a "size 30"

It's been almost 15 years since I did the seats in my Daytona, but I did contact Legendary about some spare buttons, and they managed to ship me some....so I'm thinking that they may be able to help you if you phone them directly. It's worth the try anyway.

There are multiple presses for sale on Ebay right now, but they do not all have the die sets.

It looks like you got one set of dies with this lot, if you go back to get the press make sure the dies sets are with it.

Ya, I found one on eBay close to me and I asked if they just got it at an estate sale last week but they said no they've had it all summer. Looks like I may make another visit to the lady, but I need more need more tools I'll probably never use like another hole in my head.
Appreciate the responses. Sounds like legendary has you covered.