You need to be more specific with what you're after mate. What sort of power figures are you chasing? What is your budget? What sort of power delivery do you want?

Anything in the T25 - T28 range will fit as it will have the same flange pattern. There are usually small mods that need to be performed to get each turbo to fit i.e. modifying oil and water lines, rotating housings etc. But essentially any of the turbos from this family will bolt up.

My picks -
$200 - $350 - T25G This was the factory turbo on the S13 SR20DET. They are slightly bigger so you will see a power jump with minimal increase in lag. They are very cheap but also very old so may well need a rebuild.

$500 - $800 - T28 There are several different T28 turbos with the most common being the SR20DET factory models which had either a .64 exhaust housing on the Silvia/200SX or a .86 exhaust housing on the Sunny GTi-R. The GTi-R turbo will give you more power but with more lag.

$900 - $1200 GT28BB These are the brand new ball bearing versions of the 200SX turbo and are available everywhere nowadays. Excellent turbos with a very good power/lag compromise.

$1250 - $1500 GT28RS This is commonly referred to as the Disco Potato. Exceptional turbo but possibly overkill on a CA.

This is just a very quick run down on a few of the available options. There is an absolute smorgasboard of choices available to you. It is also a great time to buy as new turbos have never been cheaper.