You can make your own neck strap and hand strap for Ricoh GR III or GR IIIx by using inexpensive, widely available paracord or shoe straps that cost almost nothing. Also, I am you how you can prevent dust from getting onto the sensor of your GR III.
NiSi 49mm Filter Adapter for Ricoh GR3
https://www.amazon.com/NiSi-49mm-Filt...
Sensei 49mm to 52mm Step-up Ring
https://www.amazon.com/Sensei-49mm-Le...
Ricoh GR III
https://www.amazon.com/dp/B08LM9BLN2