Nadya,
if 2 SELECTs give you result you want (not sure I understood what you expect,
is it 1 rec per town or just 1 rec at all?)
just combine them :
SELECT * FROM tranmstr ;
left JOIN misclndr on tranmstr.tranid = misclndr.tranid ;
inner JOIN propmstr on tranmstr.propid = propmstr.propid ;
inner JOIN sitemstr on tranmstr.propid = sitemstr.propid ;
and sitemstr.town="GOSN" ;
left JOIN bldgmstr on tranmstr.propid = bldgmstr.propid ;
right join Towns on SiteMstr.Town=Towns.Town ;
where (prefcode = "P" and Towns.town="GOSN" and SOURCE="S") ;
and between(tranmstr.extrYear+tranmstr.extrWeek ,oJC.LowWeek,oJC.HighWeek) ;
INTO TABLE &qry_arg3

BTW, what about "prefcode" and "SOURCE"?
Where are they coming from?
If they belong to inner table of outer joins (like "misclndr" or "bldgmstr"), make sure you want them in WHERE clause, not in JOIN ON.
HTH
Oleg