Can anybody tell me what years Sun Trackers had aluminum decks?
none of them.
they all have "extruded aluminum deck edging" however none of them have an aluminum deck.
make your own aluminum deck. you will need nida core or similar under it for strength, or with the typical spans you see in a pontoon, the deck would need to be thicker than 1/4" to prevent permanent oil-canning
typical sheet of 48x120 x 1/4" thick 5052 aluminum is about $450 per sheet. you will need about 5 sheets for the typical 20 foot pontoon. that is going to be on top the nida core which is about $250 a sheet.
or buy ACX plywood and for about $200 and be done