Have you asked from NECG ? They sell Recknagel -made parts and there is one model in their garderope which is very similar as in mine pre-WWII Mannlicher 6,5x57. You could find Recknagels kataloque from link below. Mannlicher style front sling swivel is on page 18 (PDF page 20).

http://www.recknagel.de/Joomla/images/stories/Downloads/Zubehoer-8-2013-web.pdf