I have done Diploma in mechanical engineering & have 8+ years of professional experience. From where can I pursue B.Tech through distance?

Institute of Mechanical Engineering is better option for you. The course is approved by AICTE. It is especially for working professional.

As of now engineering/technical courses in distance learning mode are not permitted by UGC-DEB. You can wait till the ban is lifted or go for regular/part time degree course. All the best.