South Middlesex Volunteer Rifles

[natal01]

I recently purchased a Victorian South Middlesex Volunteer Rifles cap badge together with what was described as its matching collar badge. Both badges are silver plated . I have sifted through the various reference works that I have ( Kipling and King etc.) and can find no reference to this unit, let alone a picture of the badge( s).
Can anyone point me in the right direction as to where I can find out about the unit and to confirm that the collar does tie in with the cap badge ?
Many thanks
Mike