Here the 1849 LDS edition introduced the reading “they buried their weapons of peace”, which has continued in the LDS text. This change from the to their appears to be a typo since the the in the subsequent “or they buried the weapons of war for peace” was not changed to their.
The reading “their weapons of war” is quite frequent elsewhere in the text (occurring 24 times) and probably contributed to the 1849 change from “the weapons of peace” to “their weapons of peace”. (There are also four occurrences of “your weapons of war” and two of “our weapons of war”.) Nonetheless, there are four other places where the original text has “the weapons of war”:
(In the last example, the 1920 LDS edition removed the definite article the; for discussion, see under Alma 55:16.) These examples show that in Alma 24:19 the use of the in the original “the weapons of peace” and “the weapons of war for peace” is perfectly acceptable.
Summary: Restore in Alma 24:19 the original definite article the in “the weapons of peace”, which is consistent with the definite article usage in the subsequent clause (“or they buried the weapons of war for peace”).