I'm a newbie using the manual to learn the game and it doesn't have much to say about purchase cards. How do purchase cards come into play? When you have enough gold do you purchase whatever you want at anytime during game play? It is probably obvious somewhere but I missed it and an explanation would be greatly appreciated.

You can buy cards listed in the Village space on the board. That's the basic option. There are Adventure cards Market and Market Day which also offer buy opportunities, otherwise, no buying other than Village.

Dam's right... but... my group makes Mules (not to be confused with donkeys) available in the City at a "stable." Your trouble is not uncommon, for being able to buy stuff not listed on any board space is also uncommon.

I like that Stables in the city idea, because there are times when Market Day comes up early and I can get a mule, but then never have more than 3 items for the rest of the game. While other times, I frequently need to ditch something, because of the 4 item limit and cannot get a mule.

Jon New created a City overlay with a "horsetrader" option in place of the Alchemist. In his approach, the Alchemist then becomes a Stranger card added to the Adventure deck, and he sets of a private shop wherever he is drawn. It's a nice option, and you can check it out at TalismanIsland.com.