I'd recommend you actually buy a commercial hybrid. Brown egg layer. The smaller retail hatcheries commonly sell Red Sex Links but rarely disclose the true makeup of the bird. Is it merely a red sex link they made themselves out of breeding stock on hand? Easy enough to do. Getting to the straight truth is hard, sometimes. They don't often give out that information. Their market is not very often geared toward that end.
If you really, truly want top laying birds, the ISA is a good choice, and it is still solidly in the 320 egg per pullet year territory, but it has been surpassed by some Hy Line birds, I believe. I'd do a little research on sites where commercial layers is a more common area of discussion. Hy-Line, Hi-Sex, DeKalb, Bovan, ISA, Tetra and other genetics corporations vie for producing the industry's top laying brown egger. The Hy-Line Brown is a 320 egger, and the Hy-Line Silver Brown is 330. http://www.hyline.com/aspx/productsandservices/products.aspx
Townline Hatchery, Zeeland, MI sells ISA Browns to the public. You may need to discover a retail connection for some of the other varieties.
Hy line brown is a better choice than the silver brown in my opinion, because of the feed to egg conversion rate.