How to obtain NIOS Intermediate Passing certificate after many years?

It should be available. You have to contact the school with your provisional certificate and apply in writing explaining the reasons for not taking the original certificate all these days. Based on the school rules you may have to pay some amount towards late fee. As you require this urgently personally going and contacting the school is the best option.

A. You need to collect your NIOS Intermediate certificate which should have been done 6 months after passing the exams. After doing some background check, Ishan International Public School is listed as a study center for NIOS in Patna, Bihar.

B.You can get this done by

With a copy of all the doucments related to your intermediate enrollment, passing etc approach the study center administrative office, they would be able to help you or guide you at least.

C. The other thing you can do is contact the Regional office for NIOS of the various states (http://www.nios.ac.in/contact-us/regional-offices.aspx). For Bihar it is
Dr. Sandhya Kumar,,
Asst. Director,Regional Centre NIOS-Patna
Lalit Bhawan,
Ground Floor,
Patna-800001
Bihar
Tel: 0612-2545051
Fax: 0612-2545470
Email: rcpatna@nios.ac.in
This office should be able to help you once you provide your details.

D. Lastly, since it is more than 8 years, you can apply for a duplicate copy of the pass certificate for your intermediate. The charges are around Rs 200.00 and the contact authority is
The Section Officer,
M & M Branch,
National Institute of Open Schooling,
A-24/25, Sector -62, Institutional Area,
NOIDA, UP-201309.

E. You can find the details at this link(http://www.nios.ac.in/student-information-section/procedure-for-obtaining-duplicate-certificate.aspx)
What you need is
1.The general application form to be duly filled can be downloaded (http://www.nios.ac.in/media/documents/migcert.pdf)
2. Original affidavit signed by a 1st class magistrate ( the format is in the second page of the general application form itself)
3. ID proof of your self and the certificates from NIOS
4. For postal delivery, you need to pay Rs 50 extra.

Which ever mode you use, please state clearly your roll number, exam date, the pass certificate number etc.
Keep the acknowledgments of any fax or email handy so that you can contact them for further clarifications.

As a long time has passed, you will have to go now for the process of getting it as a duplicate copy.

You will be required to give a legal affidavit stating that you have not received the same so far and you require a duplicate copy now. In your application you have to mention your details etc and some authentic document for your identification showing that you are the genuine person asking for it.

If they tell you that as per their records they have already dispatched it to you then you bring this aspect also in your application that you never received it and now as you require it, you are applying for it.

After that you will have to deposit the fee for this work as prescribed by NIOS.

As it is an old case it isvisable to pursue it personally otherwise it will be delayed.

The original certificate will be held by the institute where the candidate has studied. It happened in my daughter's case where she got the admission in Engineering based on the provisional passing memo issued by the state Board. We too have forgotten to collect the original Intermediate Passing certificate and approached the college after three years. On production of the hall ticket and copy of Transfer Certificate, they confirmed that the Original is available with them and levied a Penal fee of Rs. 500 per year for the delayed collection of the certificate as per their norms.

Therefore, the same procedure would be followed with some slight variations in respect of NIOS too and you may approach the authorities concerned to get your certificate.