Some classic antigens with varying and contested degrees of specificity are CX3CR1, F4/80, Csf1r, CD11b/OX-42 among others. More novel ones are P2YR12 and TMEM119. There are well-cited and characterized Abs against most or all of these proteins that have been validated for IHC in paraffin embedded sections.
Alternatively, you can try to stain with tomato lectins or even the original silver carbonate method from del Rio Hortega...