Hi Prasad,
According to your post, my understanding is that you want to get lookup values from another site collection.
I recommend to use rest service to get the values form the other site collections, and then set the values to the lookup column.
Here is a similar blog for your reference:
http://www.hamishking.com/2010/07/16/referencing-lists-from-external-site-collections-cross-site-collection-lookup-with-rest-and-the-dvwp/
http://bramnuyts.be/2011/04/11/creating-a-cross-site-lookup-field-without-code/
Besides, you can use Cross-site Lookup for SharePoint 2013 solution:
Cross-site Lookup Column for SharePoint 2013 and SharePoint Online in Office 365 - CodeProject
Best Regards,
Lisa Chen
TechNet Community Support
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