the stores mentioned do not carry such a product. you can find the glue at a specailty plastic store. just e-mail me and ill give you there name as i dont think were allowed to promote stores on this forum thingy.
If you've never worked with acrylic before, you should definitely do some practice joins before you do your final project, as working with Weldon #3 is the best, but also the hardest to get a good finish and seal if you're not familiar with acrylic joining techniques. Brian Ferguson is teaching a class on acrylic joining techniques through #reefs I believe, you might want to check some of the archivers there as well for some good tips on these techniques.