Eventually, if you decide to place real trades with real money, you'll need a data feed. Why not get the data feed now, before you start trading, and do a bit of research?
You can use historical data (volume, open interest) to assess liquidity. You can also use it to assess diversification (correlation to other bond futures, correlation to the S&P 500, correlation to gold, correlation to the dollar, etc).
I think your research will reveal that futures contracts on a variety of non-US bonds offer acceptable liquidity (acceptable to YOU, which is all that matters) and adequate diversification. Take a look at the bond futures that trade on non-US futures exchanges such as LIFFE, EUREX, SGX, ASX, TSE, ME. Many pros trade these; why not you?