I doubt you'll find one long enough. When I started in the bike business chains were typically sold with 116 links, which later went to 114, and many today are only 112. The bet thing you can do is find someone who rides a tandem or recumbent, and partner up to buy matched chains, and split them. They also need multiple chains, and always have short lengths to spare.

You might go the other way and partner with someone riding a 3/32" fixie. He won't need 112 links, and can spare you a few inches.

Or you might make a buy of multiple chains, keeping spares for the future, so that you'll be able to always make up your chain with identical extensions.