To get these seams right, the piece must be run through a surfacing machine after glue-up. Otherwise it's a crapshoot whether or not it's flat and invisibly joined. If I were doing this job for paying customers, I would make an appointment for a session on the thickness sander at the local mill.
There's good reason why wood counter top manufacturers charge an arm and a leg for the oversize work.
Casey

48'' x 60'' available at the link.

(Remember that you need overhang for the countertop.)

Here is a link that might be useful: Wide Butcher Block

BINGO - Here's your answer, found this today on another thread and they helped me out bigtime.

http://www.hardwood-lumber.com/butcherblock.html

They have your size - look under pricing. I called and they will custom do any size you want. We have a large island and they will do any size. They are super affordable at around $28 sq foot shipped and comes with any edge for only $35 extra!!

BINGO is right! That's awesome. Thanks so much for your help!

John Boos also has a variety of sizes and species for butcher block. I almost ordered from them but had my 4x6x1.75" island top made locally.

Here is a link that might be useful: John Boos- for various species/sizes butcher block

I found John Boos to be a disappointment -- their local distributor took my info and didn't call back. I ended up finding a vendor on ebay to make me a custom walnut counter at a great price (less than $250 incl. shipping for a 31x25 counter and backsplash). They've sent me pictures, and they're beautiful, but the counter itself is on its way and I look forward to seeing it (touching it!) in person. I don't think they do sizes larger than 4 feet, but I'm happy to share their info once I get the item and can verify the quality in person.

So there's lots of options out there.

I'll vouch for Hardwoodlumber.com, I have had multiple dealing with them, and they are fine people with a fine product who will bend over backwards to help you.
If you're in the east, shipping won't kill you as it would to go from them to, say, cali.
Casey