CASA ::

My question is that are there any games presumed lost? Like games that were suppose to be released but never were? And if so is there a list? The reason why I ask I like to hunt down old/rare games at pawn shops, flea markets, antique stores, etc.

Yes, there seem to be quite a few. I'm mostly familiar with the Spectrum titles that have gone AWOL. On other formats it often gets tricky to distinguish between lost titles and ones that simply never got a release.
As for a list.... hmmmm.... I don't have anything readily available.

Anyone else?

A few games I've never found are actually a serie of three adventure games published by Hal Renko (Kasper Boon) . See the links for more information on each game. The games were published in books and could be typed in, but also were published on tapes for the persons who didn't wanted to type the very long listing. They were written for several platforms.

The Antagonists
I own the Dutch C64 book and a working copy of the Dutch ZX-Spectrum version and C64 version of the game. The English version however I've never been able to locate.

The Secret of Arendarvon Castle
I own the Dutch C64 book and the English C64 book. I own a working copy of the Dutch and German version for the C64. The listing in the English book contains some bugs which makes it impossible to play. An erratum for the book was released but alas this didn'nt solve all the problems. The version published on tape should work allright though, but I've never managed to find a copy.

The Seventh generation
I never seen the book or the game. Any info would be nice.

There's a UK website dedicated to unfinished and/or unreleased games. They are focused on the C64, and not only adventure, but every kind of games - although you may also find a few interesting titles over there. I only found them nearly half a year ago, when they "recovered" an unfinished game I had been working on before (Angel of Hell 2). They are called as "Games That Weren't" (or simply GTW) 64. See below:

http://gtw64.co.uk/

Commodore Free Magazin is partly a similar source this way, but in a PDF newspaper format ( http://commodorefree.com/ ).

The Dragon Archive lists some rarities in the Dragon (thirty years old this month!) world. The entries that are of interest to adventurers are already mentioned at CASA, being The White Cliffs of Dover and Juxtaposition II - Usurper of Rune.

@IstenNyila and the OP: GTW is a terrific site, and Frank Gasking is doing a great job of maintaining it. But it's mostly games that didn't make it as far as the publishing stage, and so the chance of them turning up at flea markets or similar is probably very slim. But it's still a chance, of course. So plan accordingly & happy hunting

And don't forget to let us know if you come across anything interesting!