In my community there are organic farmers who let people "buy in" to their farms. You typically pay a fee, and then contribute a certain number of hours a week helping tend their gardens. You get a share of the produce. It's a great solution both for apartment dwellers and people who can't garden for other reasons (e.g. heavy metal contamination). I wouldn't be surprised if many of these growers share RG's concern about seed stock and would be willing to work with you to set aside some seed every year.