There are three main sources for Tavor SAR hand guards, rails, and aftermarket accesories. Midwest Industries, Manticore Arms and Gear Head Works. Geissele has the Super Sabra and trigger bow for the SAR. I have the Super Sabra and really like it.
Midwest Industries.
https://www.midwestindustriesinc.com/MI-Tavor-Extended-KeyMod-Handguard-p/mi-tkhx-blk.htm
Manticore Arms
https://manticorearms.com/product-category/parts/forends-and-rail-systems/page/2/
Gear Head Works
https://gearheadworks.com/store/page/3/?filter_gun-model=iwi-tavor-sar
A good source for all things Tavor whether SAR or X95 is the Bullpup Armory. BA also carry the Shooting Sight Tavor SAR Trigger which get good reviews.
https://www.bullpuparmory.com/IWI_TAVOR_s/1900.htm
IWI US have parts kits and aftermarket parts sold by other vendors.
https://iwi.us/product-category/tavor-sar/