Ability to have unique sequence number for specific type of records

Summary

To have unique sequence numbers for records with specific type

Content

Requirement:  For SRs of type 'X'  we have to have continuous numbers (unique sequences) for legal purpose.  currently we have SR number in SR object which is the PUID, but this is for all type of SRs.  So, in this way type 'X' SRs we can have sequence number gaps, which should not be  as there is a periodic report to be submitted to Governmnent and for this type of SRs and there should not be gaps in the sequence numbers. 

Is there a way to achieve this requirement?