I found that with a backdated search on EF (it was created on 12/6 and pulled on 12/7). But there was actually a duplicate one-way fare with same price -- GAK2AQBS. Note the "OW-ECONOMY" designation.
V FARE BASIS BK FARE TRAVEL-TICKET AP MINMAX RTG
1 GAK2AQBS N‡X 34.00 E05JA T07DE 21/1 -/ - 595
R09MR
PASSENGER TYPE-ADT AUTO PRICE-YES
FROM-SFO TO-SAN CXR-UA TVL-02FEB22 RULE-BSQ1 DFR/11
FARE BASIS-GAK2AQBS SPECIAL FARE DIS-N VENDOR-ATP
FARE TYPE-EOU OW-ECONOMY OW UNBUNDLED
USD 31.63 0595 E05JAN22 D09MAR22 FC-GAK2AQBS FN-GB
SYSTEM DATES - CREATED 06DEC21/1913 EXPIRES INFINITY
PUBLISHED RTG SFO-SAN/UA595 /TAR-DRG1 EF-06DEC21 DIS-INDEF
MAP CONSTRUCTED LEFT TO RIGHT AND RIGHT TO LEFT
1. SFO-LAX-SAN
.
This is what a fare with a roundtrip booking requirement will look like (SFO-SGU example). There is no matching one-way for this. In short, the legacies all still have domestic roundtrip fares out there. But they are basically limited to routes where there is little or no LCC competition. If you live in a metro area with a lot Southwest/Alaska/JetBlue service (who only have one-ways), you will rarely encounter them as the legacies will match their fares. A counter-example is DTW (with limited LCC non-stop service), which has numerous domestic roundtrip fares on DL due to lack of compeition. The fare differentials are generally not all that great these days so they are not that noticeable when pricing out fares.
V FARE BASIS BK FARE TRAVEL-TICKET AP MINMAX RTG
1 TRK2AFEN T R 172.00 ---- 21/1 -/ - 578
PASSENGER TYPE-ADT AUTO PRICE-YES
FROM-SFO TO-SGU CXR-UA TVL-02FEB22 RULE-ECF2 DFR/11
FARE BASIS-TRK2AFEN SPECIAL FARE DIS-E VENDOR-ATP
FARE TYPE-XRN RT-RT INSTANT PURCHASE NONREF
USD 160.00 0578 E23JUL18 D-INFINITY FC-TRK2AFEN FN-L
SYSTEM DATES - CREATED 07OCT21/0958 EXPIRES INFINITY
PUBLISHED RTG SFO-SGU/UA578 /TAR-DRG1 EF-07OCT21 DIS-INDEF
MAP CONSTRUCTED LEFT TO RIGHT AND RIGHT TO LEFT
1. SFO-DEN-SGU
.