Many car holders are available in accessories:

https://lapmonitor.com/store/en/13-accessories

Some transponder mount are available for printing

https://www.thingiverse.com/LapMonitor/designs

Buggy 1:10th

B6.1 Transponder holder

XB2 Transponder holder

Other 2WD examples

XB4 B74 YZ4 Transponder holder

Buggy 1:8TH ECO

Mugen MXB7/8

XRAY XB8e

TLR-XE

Buggy 1:8TH nitro

Generic solution

KYOSHO MP9/10

XB8