OT Somewhat - External Battery Posts?

On a variety of vehicles, mostly emergency ones but also
motor homes and RVs, I've seen two external battery posts,
each about 1" in diameter and 4" long, mounted about 4"
apart, near the front or rear bumpers (sometimes elsewhere).
One is covered with a black rubber sleeve, and the other
with a red rubber sleeve. Both can be removed easily for
attaching jumper cables to provide (or receive) assistance
to (from) another vehicle. Internally these posts are
connected to the battery.

Where can these be purchased? I've tried all the auto parts
chains, NAPA, RV dealers, and various truck stops. Everyone
seems to know what I want, but has no idea where they are
sold. Any ideas?

Thanks.

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CWLee
Former slayer of dragons; practice now limited to sacred
cows. Believing we should hire for quality, not quotas, and
promote for performance, not preferences.