hear this at least 1X per week. i'm sure he means well but your "shop guy" is absolutely wrong. in the most simplistic terms here's the real deal:
buell electronics such as wiring looms, switches, switchgear, ecm's, lights and all else very common and very well built components. most sourced from popular jap suppliers such as nissin. in my collection of vintage and modern bikes are a few 45 year old jap bikes with virtually the identical components. they still work flawlessly.
other than transluscent body-work...think kick ash/orange krate/hero blue/cherry bomb components....there will never ever be a shortage of parts available. if and when that time comes the aftermarket will kick in and reproduce the part and fill the void.
every single perishable and service related item on an XB will be available FOREVER! no exceptions.
there has always been a short-supply if you will of knowledgeable, competent trustworthy buell techs. that won't change. fortunately we're not talking garbage pizza bike desmo valve train adjustments here. a competent local sportster mechanic can do 90% of all the work any XB might ever require.
these are simple fairly bomb-proof bikes that are relatively easy to keep on the road. that will never change.