Is the supply of Sun Rhyno Lites drying up?
 

I'm noticing an increasing scarcity and a corresponding rise in price of what there is. Anyone else notice this?

They still show up on the Sun-Ringle website MTB | SUNringlé so I doubt they've been discontinued.

You may be seeing the cost increase due to cost of materials/labor increasing. As to scarcity, it's a rim brake rim in an era of increasing disk brake popularity. Manufacturers are specing disk brakes on every type of bike now: atb, cyclocross, and road. New buyers seem to be embracing disk as an upgrade over rim brakes. As with my lugged steel road bike, you will pry my v-brakes (admittedly more modern than cantis) out of my cold dead hands.

Sun has changed owners a few times. . . . some lines look to be dropped.

Mavic has some reasonable matches, for 700c I find the a319 to be similar weight and strength.