I've recently raised the same question on various Facebook groups trying to find information. Also asked Acocks Green Local History, no reply as yet, they have a page on their website all about Station Road and it's history, no mention of Pax, also contacted the National Motorcycle Museum but they have no information. It was short lived, only a couple of years. The did have a stand in 1921 at the trade fare at Castle Bromish/ Vale. The area around Acocks Green at the time I can only assume the postman knew the businesses so Station Road was all that was needed.