A320 type rating
 

I'm currently holding a Srilankan CPL/IR Multi endosement with ATPL subjects. I want to do a type rating on A320 in USA. Do I need to ATP course as well. Or is it possible for me to do just the type rating in the states?

Well, the main question to consider is, does the State which issued your CPL license (Srilanka) approve a TR which is issued by the FAA (US)? Because some countries won't - e.g. the EASA (Europe) doesn't except FAA issued TR for certification purpose. However, if you hold an FAA license besides your Srilanka license, then you could add an FAA TR on your FAA license. In this case you should refer to the minimum requirements for a TR as stated by the TR provider (usually this info can also be found on the website). But I assume that for an FAA TR one must hold at least a R-ATP (R=restricted). Generally speaking this means that you need 1500hr and 200hr x-country time. See link(s) below:

The 1500 Hour Rule - Restricted ATP Requirements for First Officers Boldmethod

FAR PART 61.160 Aeronautical experience - airplane category restricted privileges
(f) A person who has 1,500 hours total time as a pilot, 200 hours of cross-country flight time, and otherwise meets the aeronautical experience requirements of §61.159 may apply for an airline transport pilot certificate under this section.
Source: https://www.ecfr.gov/cgi-bin/text-idx?SID=45a1929b57508020762a6dd7a163deb2&mc=true&node=se14.2 .61_1160&rgn=div8

Nay,
You don't have to do ATP. Just ask Sri Lankan CAA if they recognise FAA type rating training
​​