I know of two LM Ascent Engines still in existence. I believe Grumman built 13 Lunar modules. I also think at least 5 engines were tested at White Sands. So that is 18 that were built at a minimum. But I suspect more were made for testing. The LM that made it to space did not return so they are gone.
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2$\begingroup$ Have a look here. 15 LMs were build, 10 were flown. $\endgroup$ – Uwe Apr 4 at 13:18
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Things that don't count, but could be confused for engines:
Four "breadboard articles" BA-1 to BA-4 were built as prototypes of the plumbing. Three of these were used to feed engines during testing on HA-1 to HA-3.
PRA-1 to PRA-6 were more advanced plumbing prototypes used on PA-1.
HA-1 to HA-4 were "test rigs" in which ascent engines could be mounted for testing. HA-3 was used at White Sands for firing tests.
PA-1 was a test rig used at White Sands to test a complete setup of ascent engine, RCS quads, and their tankage and plumbing.
LTA-1 to LTA-8 were "lunar test articles". Tests included fit checks, vibration, thermal limits, vacuum chamber, electrical compatibility, and electromagnetic interference. LTA-2 flew unmanned on a test flight of the Saturn V booster. LTA-5 was used as a test rig at White Sands.
Actual engines:
With flight-qualified engines, 57 tests were conducted over a total firing time of 3392 seconds. Five engines [LM-1 to LM-5] and six thrust chambers (three heavyweight and three lightweight) were used.
LM-1 was used in a lot of testing at White Sands, and then flew unmanned in LEO on Apollo 5. Burned up in Earth's atmosphere.
LM-2 was tested at White Sands, then drop-tested. It's now the LM on display at the Smithsonian.
LM-3 was used in a lot of testing at White Sands, and then flew manned in LEO on Apollo 9. Burned up in Earth's atmosphere.
LM-4 was tested at White Sands, then flown in the "practice landing" of Apollo 10. It is now somewhere orbiting the sun (exists, but exact location unknown).
LM-5 was tested at White Sands, then flew on the first moon landing, Apollo 11. Crashed in an unknown location on the moon.
LM-6 was used on Apollo 12. Deliberately crashed into the moon.
LM-7 became Apollo 13's "lifeboat". Burned up in Earth's atmosphere.
LM-8 was used on Apollo 14. Deliberately crashed into the moon.
LM-9 was never used. It's now the LM on display at Kennedy Space Center.
LM-10 was used on Apollo 15. Deliberately crashed into the moon.
LM-11 was used on Apollo 16. Deliberately crashed into the moon.
LM-12 was used on Apollo 17. Deliberately crashed into the moon.
LM-13 was supposed to be used for Apollo 18. It's now on display in Long Island, NY.
LM-14 had a complete ascent engine, but the rest of the vehicle was never completed for Apollo 19. Available.
Some parts of LM-15 for Apollo 20 were produced, but not a complete ascent engine.
So 19 complete engines produced, 5 still in existence, 4 on Earth.
