Ahhh young Padawan....but all these old AMT Star Trek kits are new again, and all to be re-released by Round 2 in the near future, including an all clear Enterprise D kit, to aid in easier lighting of it.
How did I acquire my kits. Bought alot on Ebay (before I got into the business itself), LHS and such.
Then I became the LHS, which depending on how you look at it, is a blessing and a curse, because you could now have that elusive kit you always wanted at cost now (providing it was still being produced), however, it makes it all too easy to "just add an extra for yourself" when doing the orders.
I think my personal stash has gone from about 300 to between 500-600 in the last 3 years I have been open. I however don't buy as many on Ebay anymore, only those that are long out of production, and they are cheap......usually those 2 don't go together, but every now and again you get lucky.
Some currently I look for. Back in the late 60's early 70's, Tamiya had a selection of 6, 1/18 car kits. This was before they ventured into the 1/12 cars. I picked a Porsche 910 Le Mans

car up on ebay for a paltry sum of $30 with shipping. I get the box home, and it is really quite a nice kit, not up to today's standards, but for 1969, it would have been very well detailed. On the side of the box it showed some other kits in the series, 3 other Can Am cars, and 2 street cars. Well the street cars were ugly, some little Subaru econobox I had never heard of, and a little Honda econobox (smaller than the civic of that time).
I have since gotten one of the Can-Am cars, the Lola T-160
and continue to look for the other 2, a Nissan R381

,
and the elusive McLaren M8A

I have seen the Nissan listed on Ebay occasionally, but have never seen the McLaren. These kits were re-released in the mid to late '90s, with the exception of the McLaren. Rumors as to why it wasn't re-released run the gambit from not having the licensing, to the molds were either damaged or lost. Thus, it is the hardest to find out of the 4.