well, on the internet, there are 3 to look into:
BlackMagic,
AJA Kona card
(there's also the AJA iO in/out box, but that's overkill for what you need)
Aurora Pipe
they've all got super-basic SDI versions.
pick the one with the most of what you like,
or the cheapest, if you like that more.
And find the one with dealers closest to you.
nick