This is a really sophisticated cocktail. I have used red currant jelly which I dissolve into the kirsch. But David Embury's raspberry substitution works nicely too.
This was a revelation. Now I finally know what to do with Kirschwasser. The basic template here with Kirschwasser playing a supporting role to vermouth in a lower ABV cocktail provides endless possibilities for improvisation. I used homemade grenadine instead of groseille syrup because that is hard to come by in the USA.
If you can find red currant jelly that is only made with red currant juice and sugar (obviously there will be pectin), try dissolving that in the kirsch by stirring. Then add the vermouth and ice. Stir that and strain through a fine strainer. Also, David Embury's substitution of raspberry syrup works very well too.