Hi again Phi,
You have to match the max current, max voltage, and the gate current for
all four quadrants. The gate current spec varies wildly so you have to be
careful there and check each quadrant. Of course if you are doing a
repair and not a new design you have to match the package type too
or it might not fit into the exisiting product without massive mechanical
modification
I found what looks like a cross reference: NTE5629
which Mouser carries. You could try there or call Digikey and see if they would
part with a quantity of 1 piece.
BTW, what is the shipping price from USA to the UK? I ask in case i can
get one myself, but in the past i had problems mailing to various places
in the world. For example, i was mailing a special serial port AD converter
chip to Australia, and found that the shipping was high for priority, but
only about 2 bucks for first class, but the guy would have to pay me in
US dollars (USD) because my bank charges 50 dollars for conversion from
AU dollars to US dollars. I ended up sending it for free or it would have
cost me 40 dollars for conversion ha ha.