Maharashtra

For admission in Polytechnic course after 12th (Science) you need to crack an entrance examination called Diploma entrance test, otherwise can join any private institution that perform their own Diploma qualification test. After joining there is a branch selection in which you have to a specific branch like mechanical. Following are some top colleges where you can apply:
All India Shri Shivaji Memorial Society Polytechnic
Anjuman Polytechnic
Bhandara Polytechnic
Acharya Shriman Arayan Tantra Sansthan
Amrutvahini Polytechnic
Guru Nanak Dev Polytechnic
Meera Bai Polytechnic
Tool Room & Training Centre
Arya Bhatt Polytechnic
Gobind Ballabh Pant
Kasturba Polytechnic for Women
Aryabhatt Polytechnic.

Hello Anjalika,
I am afraid your dream is not going to come true. This is so since Maharashtra along with many other states restrict admission for engineering colleges for first year at well as for lateral entry for the students who are domicile of that state. You are doing diploma from a college in West Bengal and it seems that you must be domicile of West Bengal. Hence for you to get admission in a government college is next to impossible. You need to look for getting admission only in West Bengal. However, for detailed information I would suggest you to visit the website of directorate of Technical Education Maharashtra and download their information brochure for lateral admission.