Getting 4 corners weight has been a real problem for me. Haven't got it done yet. HOWEVER...
If you can find a truck maintenance place that uses VIS-CHECK you can get it done there.
VIS-CHECK vis-check | VisCheck Service Automation
This can be a two-fer. The system is an undercarriage diagnostic tool that can check steering linkage, braking system and stuff like that. No, it doesn't do wheel alignment.
My local International truck dealer has one a will let me run my rig over it for getting the weight only for $25 and $50 gets me the full diagnostics. I'll probably opt for the full diagnostics. Some places will waive the fee if it shows you need work done and have it done there.
As long as you have your tow bar on the rig, I don't see how having the toad also attached makes much of a difference there. What I am considering doing is running my rig through the VIS-CHECK and when done, attach the toad and run over to a near by CAT scale to cross check the rig weight and then get the toad weight. If it all cross checks, my total front and rear axle weights should match the VC system withing a few pounds. If there were some major change to my rear weight caused by the toad set up, I will be able to see that. Again, I just don't see how a hitch weight distributed between the rig and the toad will change wheel weights on the rig to any serious degree.
Don (RVM22) & Sandee (Biped Humans) plus Gunny & Thor (Quadruped GSDs)
2006 DSDP 4320, 2013 CR-V, Blue Ox Aladdin, Air Force One.
Clearly a DP NOB but willing to learn!