Beard in the Sky said:The DM should never "go out of his way"
Of course he should, he goes out of his way all of the time. He makes the adventure, helps out players by placing plot hooks here and there, comes up with 'random' treasure, decides goals and motivations of everyone around them. Sometimes things will work out well, sometimes poorly, but one way or the other the dm is always 'going out of his way' to do something.
In this case however, the character tried to do something, spent feats and time (it sounds like a pretty good amount if he got sick of it) along with funds to try to do something. That isnt, 'going next door to the dungeon to get the weapon' this actually involves things.
The dm always has exotic people and places that can and do pop up. Sometimes there might even be a guy who 'randomly' has something one of the pc's really wanted, nothing wrong with that. One of the bad guys might even use just the weapon that the character wants to, nothing wrong with that either. These are all things to make the game more interesting and more fun, it could be that this bad guy somehow gets away.. but the pc has hope of meeting up again and getting that really cool weapon.
This is all good. However, spending feats on something, spending time and money, and in the end having to give up in frustration. That is bad.
It is still a game after all. There are a lot of variables. Even if the weapon is incredibly rare the chances of the pc's coming across one of them increase greatly as time goes on. If there is only one spiked chain for every 100 other weapons then by 9th level the pc should have seen at least several, of which probably all of them were enchanted, since they are rare people will commision them specially and those tend to be enchanted.
The game moves on, and all of this is spelled out in the dmg that you are talking about. Trying to let everyone have fun is a good thing. Punishing a character for picking a certain feat is generally a Bad Thing. Every now and then? sure, go for it, have a ball. Just like being captured and having no gear or being in an area of antimagic. These things happen, but they should be more rare than common.