The sources for mohair and broadcloth car fabrics are becoming few and far between.
Try Classtique, they’ve expanded into wool materials. Some of their pricing is interesting.
https://www.classtiqueupholstery.com/index.php/hardware-yard-goods
SMS is mentioned often but seems hated, as they’ll take your money and give you promises, but sometimes years to deliver. I’ve heard that they try to build up orders then get a run of material done to meet the orders, rather than the other way around. This whole paragraph is hearsay.