Where to find genuine heavy-duty ball-mount springs?

I have a Kia Sportage and it has a standard, side-mounted spring mount located on the rear left of the vehicle. Using the newer types of helical whips, I don't have any mechanical issues. However, when I try and mobile using my superior Webster Bandspanner antenna, the thing whips all over the place. It appears to me that the new springs I currently have a not nearly as good as those I've had in the past. This same antenna, bumper mounted on a '68 Mustang, had no issues, whatever. Are there truly heavy-duty springs out there? de K3HVG

 

The best you can get:

https://breedlovemounts.com/

...DOUG
KD4MOJ

 

I got lucky and found an NOS Antenna Specialists spring at a hamfest for $10 -- but if you can afford it, here is the spring for you:

http://www.cal-av.com/springs.html

 

As the link above shows, these springs are the best available, and I do use one as seen in this photo of the rear of my mobile.
The one I am using is the Mark 5


Jerry VE6AB

 

most newer car have tow hook attachment in front and back of car. they are very strong for towing of car. and that probably also make good antenna mount ?
some of the tow hook are made to attach to "U" shape Tie Down hook on car for transportation.