1. Google is your friend. Shell has a list of stores that carry T1. Tractor Supply stocks it. It's available for order.
Detroit Diesel 2-strokes require it and cannot use multi grade. Since there are a lot of these engines still in service*,
it should be available for a long time to come.
*Applications include gensets, marine, and motorhomes as well as some older trucks and construction equipment.
Around here a lot of the shrimpers still run a 6-71. Motorhomes use 6V92, 8V71, and 8V92s. Old Bluebird, Prevost, and Newmar
all used them.