In addition to making half-bitcoin and one-bitcoin pieces, Nolacoin (“The Bitcoin Exchange of New Orleans”) also made a three-bitcoin piece, and I picked one of those up back in 2014.
It’s a beautiful coin, with a two-tone color scheme of mirrored silver in the center and a golden outer margin. Like the other denominations, it’s plated brass and not precious metal, but that doesn’t change how pretty it is. It is the same size as the half and the one, and also features the public address, the private key and a QR code of the private key laser-engraved into the metal of the coin.
Nolacoin has long since stopped making coins, but at least he left us some remarkable designs. While there are some 5 BTC pieces out there from various manufacturers, this is the only 3 BTC piece that I’ve come across. It’s a big coin with a big denomination, especially at today’s exchange rates.
Standard disclaimer: It’s always, to some degree, a bad idea to let anyone else have access to a private key which controls any of your bitcoin wallets; in a sense, it goes counter to the bitcoin system itself. Once someone else has handled the key which controls your funds, you have to trust both that they exercised adequate security procedures while handling your key, and that they have not save copies of your key to exploit at some point in the unforeseen future. While some (such as Mike Caldwell of Casascius) have established trusted reputations, newer operators can only prove their trustworthiness over time.