I find the kind of people/relationships which turn into cofounders to be fairly rare. It requires mutual trust and respect, as well as passion for a shared goal. I've only met 6 in the last 22 years, so I'm no expert on how to meet one, but what has worked for me are two things: exposure (that is, spending time with people, preferably doing something that might garner respect and trust) and sharing your passions (talk about your ideas, and see who thinks they are cool).
If you are introverted, getting exposure might be difficult. Make sure you spend time around or working with people who might make good cofounders. Doing similar work to what your ideas are raises the level of technical trust (e.g. if your ideas involve web programming, work together to show each other that you can do that well), and if you are a trustworthy person, given enough time that will show through as well. Some kind of 'forced' social interaction (such as school, day job, roommate, family) is helpful if you are very introverted.
Sharing passionate ideas usually isn't a problem, at least for me. It's getting me to shut up about them ;). This annoys many people, but it makes it very easy to pick out the few people who are interested in them too.
I think that if you are feeling that working alone is non-optimal, you are probably right. I know I am much more productive as part of a team. The hard part is that you really do need to be picky about who is on your team if it's a real project. On the other hand, if you have a few 'what if' ideas you are willing to throw away if it doesn't work out, you can take a few risks with possible cofounders to see if there is chemistry there.