what if a colleague (who is still working in that organization) writes the letter......as my supervisors have either left or transfered to other cities?This is a very common issue. If you search on the forum you will find many people who have faced this problem. And several opinions.
1. try to get it in writing from HR / Company that they have an official policy of not issuing letters with job duties.
2. get a senior / your line manager to write a letter detailing your job duties. (as far as I know, there is no need to notarize but it could be good to have). Make sure he puts his contact details and position on the letter.
3. attach your colleague's name card for more credibility.
4. you can attach print outs of the job duties mentioned on the ERP system. Did you say internet or intranet? because if its available online for everyone to see, you might as well attach the link to that in your LOE.
5. explain in the LOE that your company wouldn't issue you a reference letter with job duties.
Quite a few people have submitted application in the above way successfully.
good luck.