Sir i have 3 years of experience from the first organization which was NGO non government organization but i can provide all the details/proofs of the seminars and workshops that i have attended which were organized by donor agencies i.e USAID, British Council and Citizens Foundation who funded our organization and they still operate. While i have only1 year of experience from the last organization.
I highly doubt that proof of attendance at seminars and workshops will be enough proof for IRCC with regard to documenting that particular work experience.
Again, the general alternate documentation that IRCC will consider accepting is a notarized letter from an ex-manager or colleague outlining the details IRCC asked for (your employment dates, job title, annual salary and major benefits, job responsibilities and duties, etc. - the job responsibilities and duties being one of the more important things that need to be outlined). It would also be a good idea to attach your initial contract of employment/offer letter, your relieving letter/separation letter if you have one, and pay slips. You would also need to provide a letter of explanation (LOE) explaining that the organization has closed, and this is why you are providing these things in lieu of the reference letter.
If you can't provide these things in lieu of the requested reference letter, you can't claim the work experience, and will only be able to use the 1 year of experience from the last organization.