I made a similar mistake in one of my first milling projects 
1F offers spare shoes, SVGs for the shields but if you broke the side arms (I did) your options are instant glue, ordering a full kit or designing and milling your own replacement…
I had started designing replacements side arms when then they released the infinite dust collection (which seems to have disappeared from the store…) so I eventually got brand new side arms…
Let me know if you’d like me to share the draft project (Fusion 360 for 12mm Delrin). Warning: it’s close to final but not 100% tested yet.