I've set up a little service that allows you to buy testnet4 bitcoin:
https://testnet.sale/. It's working as simply as possible. You enter your testnet4 address, choose an amount, send BTC and once it gets one confirmation, the server automatically sends you your tBTC.
The reason I built this is that the Altquick exchange announced that it temporarily suspends trading altcoins, including testnet, and that it might be shutting down. This is the only exchange that allows buying and selling testnet4 coins, so if it does shut down, it'd render it practically infeasible to buy and sell large amounts of testnet.
Important disclaimer: Testnet's purpose is to allow developers and enthusiasts to test the bitcoin network for their applications, and thus, are worthless at the margin. Their purpose is to be tested and potentially be lost/burned at development instead of real bitcoin. We do not refuse this reality. However, for the vast majority of tasks, a minimum amount is sufficient to test the network. These amounts are freely given away at faucets like
faucet.testnet4.dev. It is only for a small minority of tasks where thousands of testnet coins might be needed. It is also increasingly difficult to obtain these large amounts, and therefore natural for a market to form around them. You can disagree with this assertion, and insist that these large amounts must also be given away for free, but economic reality has proved otherwise; there exists a set of people who are willing to buy them, and a set of people who are willing to sell them. We believe that serving the voluntary transactions of those people embodies the ethos of bitcoin.
The service is new, and I wrote the backend from scratch, so if you encounter any bug, you can post below, or send me a PM, or send me an email at
testnet.sale@protonmail.com.
Please note that I have more coins than those displayed as "max", but I haven't deposited them at testnet.sale, yet. You can contact me privately if you want a lot more.