In Texas, the likeliest source of rubber would be the Guayule shrub. It was (briefly) a commercial source of rubber in the early 20th century
This article may inspire some ideas
https://www.wired.com/2015/07/superp...bber-monopoly/
Let's suppose these fields of Guayole have a neighbour: a Morrow Project logistics base that's buried nearby. This base has extensive stores - but also has equipment necessary for manufacturing and remanufacturing rubber products
It might be an interesting scenario if someone (the Breeders?) discovered the details of a vast amount of "rubber plants" growing in Arizona. Bikers, Truckers and traders from Texas might also be very interested. Add rumours of a "lost cache of technology" and you have a race to find the place