So...

[RyanDOT]

1st: Can i get free T-Mobile SIM Cards anywhere?

2nd: Can i keep the same number from my Orange SIM to my T-Mobile SIM?

[Sunny.]

Question 1:
Yes
http://www.t-mobile.co.uk/shop/free-pay-as-you-go-sim-cards/

Question 2:
Yes ring your current provider [orange] and ask for a PAC code.
When they issue you this code, its valid for 28 days.
Ring your new provider [tmobile] and ask to keep your own number. They will ask for the PAC code and then give you an estimated day when it will be completed.
On the day E.g Thursday both sims will go down and they will be up the following day and then simply throw away the old sim and use your new sim.

Note: Any credit on your old sim will go so use it up before you switch.

That should answer all your questions (: