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It looks like other Mfg's used the same Caps w/ different Centers as ET pic below, maybe you can find some and swap Centers?
Coker has a few Rocket Caps although none the same as you need, the page keeps changing but there's a similar Rocket Ctr. only around page 4-7 @ this link...
https://www.cokertire.com/accessories/caps.html#p=6
Other style 5-bolt tab Caps may fit too, I just checked the tab mount hole Ctr to Ctr dimensions of some Fenton Dish Caps here and got 2-1/8" between holes 1&2 also 3-7/16" between holes 1&3.
Best of luck w/ your quest!
~ Pete
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