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.