Some offer this. CedarFX have a 0% commission option. This natually will mean spreads might be higher than say a broker like IC Markets for example. You'd need to look into both and weigh it up. I use both brokers and the lack of commission is good for longer term trading where spreads maybe aren't as important as they are when scalping let's say. As always DYOR.
If you can't spot the liquidity then you are the liquidity.
No commission would mean wider spreads. As said by @seb king, you got to weigh your options. I would always go for broker with low spreads over no commission. Finprotrading, lmfx, fxchoice are some brokers I found good in this regard. One just has to ensure that the commissions are not too high.
I also prefer ECN brokers over other types as I get the best prices for all trades I execute with them. The good part is that most brokers offer ECN accounts making it easier for traders to find a good one for them.