For backtesting on Amibroker, you can import data from virtually any source.
A handy free one is Alpari's DataBank (it goes back as far as 1979, depending on the instrument). It has Minute and Daily data, from which Amibroker can construct any other timeframe (above 1 minute of course! it doesn't "invent" quotes, as
MT4 does...).
If you use MT4, Apari also offers data in MT4 format so you can test your EA on MT4 with that data to make sure it works properly (ie catches the same trades as your Amibroker system).
Fyi, I import Alpari Metastocks format to AB through the "Import Wizard".
ForeXite is another source but if I remember, it's not convenient to download.
http://www.alpari-idc.com/en/dc/databank.php
Ogeima.