I've been using these:

https://www.amazon.com/dp/B06XWW7VX1/ref=cm_sw_r_apan_glt_fabc_0CNYGD1WNH0BZ4F4AYBB?_encoding=UTF8&psc=1)

I'm pretty OK happy with them, and I use a medium-coarse grind with my Solo II.

Trey at one point had shared with me the following link to these on Amazon: https://www.amazon.com/gp/product/B06XWW7VX1/ref=ox_sc_act_title_1?smid=A1R57E4J880IXC&th=1

Not sure if it links properly, but the ones you'll want are 1/2" (.50"/12.7mm). Or reach out to Trey at DW and he'll point you where you need to go for some. GL!