As far as my knowledge is concerned most of the brokers offer unlimited demo accounts for practicing. But try to make sure that you are using the demo accounts in the right way so that you are not stuck up with demo only.
So far I have not seen a broker that is offering limited demo account practice. I might be trading in small brokers but they are giving lifetime demo account at least which makes them better than those who impose limits.
there are small differences between demo and live, its good to start demo with small amounts, estimated amounts of the actual money you wat to trade, but then when you go live for the first time, keep it low to test the waters, hhey just open a couple of demos with different brokers, good luck