Well, These are clinical electives. People from singapore had been doing it in March and april. U r posted in the departments under some unit. Duration is 1 month each and I dont think there is any specific criteria for that. U just need to contact the administrative section. I think it would be better if you apply in 3rd or 4th year as by that time you must have developed some clinical base. I dont think any feculty will accomodate you for research for such short periods. I am not aware of any more colleges.
Have a good luck!