How can I get more than 1 BTC on testnet? The only way I know of to get testnet coins is through faucets such as the following.

https://testnet-faucet.com/btc-testnet/
https://testnet-faucet.mempool.co/
https://kuttler.eu/en/bitcoin/btc/faucet/
https://coinfaucet.eu/en/btc-testnet/

I found these faucets with a search. They seem to be actively maintained but only give 0.01 tBTC at most. Sometimes they are down or not working for me.
I would like to get at least 1 tBTC to test an application which is expecting more around 0.8 tBTC. How can I get more tBTC? I would be OK with paying for some tBTC. 1 tBTC would take a long time to collect using faucets, and I feel I am abusing their service.
There are no exchanges or services which sell testnet which I know of.
Instead of purchasing directly, mining hardware can be borrowed or rented to directly mine testnet coins. CPU mining is no longer a real possibility for generating over 1 tBTC.
The steps for mining testnet coins would be the following.

Setup Bitcoin testnet full node
Setup pool interface for mining testnet with a SHA256 miner (such as CoiniumServ or P2Pool)
Rent or borrow a SHA256 mining device to generate the coins
Get a testnet address for collecting mining rewards

Ironically, this will probably cost you time, effort and MONEY, but you should be able to get as much tBTC as is needed. Hopefully, there will be an open market for testnet BTC someday.
I also created step-by-step details on how I mined testnet coins which might be helpful.