Jointing granite cobbles

[AlanSandstone]

Hi - hoping for some advice. I have a border of granite cobbles going around an asphalt driveway. The granite cobbles were never jointed, so they fill up with dirt, and weeds grow. I’ve cleared the gaps now and want to joint them.

The gaps are uneven, and a little too wide to joint with kiln dried sand.

I was thinking of the jointing compounds, but a bit worried whatever is in them may damage the adjoining asphalt. Would it? As an alternative I was thinking to point with granite grit - say 3-5mm - but I can’t find in any builder merchants around Dublin. Any advice?

Thanks