JA Hamilton are UK based, nothing against them but there have to be others closer - maybe even local.
It does look like many suppliers of horsehair are in the UK but if it's cold and rainy in your part of the world too, spend a bit of time Googling (or maybe ebay but there's not much in North America right now) to see what you can find.
Examples:
http://www.diyupholsterysupply.com/s...-hog_hair.html
http://lefebvreupholstery.blogspot.c...with-what.html (Cornwall Ontario - the article is info but they may also supply... Lefebvre's website is blocked at work)
https://www.ebay.com/itm/Upholstery-...-/152007031053
https://www.upholsteryconnection.com...ed-curled-hair
Coir seems to be more readily available, similar in texture but originally considered inferior to horsehair.