found the info! most are FA, but it looks like there are 1500 semi AR15s that qualify as C&R.
semi rifles:
Colt AR-15 Sporter "The Viet Nam Tribute Colt Special Edition" .223 cal. semiautomatic rifle, bearing the American Historical Foundation registry numbers of VT0001 through VT1500.
select fire rifles:
• Armalite, AR 10, 1955, cal. 7.62mm NATO submachinegun, made by the Armalite Div. Of Fairchild Engine & Airplane Co., Costa Mesa, CA prior to 1961.
• Armalite AR-15, .222 Remington or.223 cals., produced by Armalite.
• Armalite AR-15, Model 601,.223 cal., mfd. by Colt. Must be marked "Armalite."
• Armalite, AR-18, selective fire rifle, cal. .223, prod. by Armalite, Costa Mesa, CA.
some very early semi AR15s should have C&R status in the coming years by the "50 year rule"
edit: to aswer your question. a couple of years ago i asked a similar question, the answer i got was that it woudl prob be easier to get a specific serial# weapon reclassified as a C&R instead of a whole class. how would you prove the collectability cut- off at a certain serial # for an SP1. it would be easier to prove that a specific weapon has collector value.