At what point does an OEM tire go from being only sold by the dealer to being marketed by other sources?

Right now the tires for my bike are "available at the dealership only" (straight from the Dunlop website). I can buy the tires at the dealer and have my Indy shop put them on for less labor.

My boyfriend can by 2 tires for his 2001 Road Glide at J & P cycles for the same amount it costs me to buy just the back tire for my bike at the dealer.

 

OEM tyres have been the same way for many years, however other brands offer the same sizes, which can be bought from a wide variety of outlets. It's possible your boyfriend's bike dates back before H-D got tied in with Dunlop (and Michelin) as they are now, hence J&P. Dunlop also offer American Eagle in most popular Harley sizes, which are widely available. Personally I've been glad to see the back of every stock tyre on my Harleys, over the last 40 years or so!