It took me <2 minutes to find multiple options for LED-ATL on October 20. These include various combinations of SU, DL, S7, TK, and BA.

DL has not served Russia for a good long time. However, here is a list of DL's current interline ticketing agreements. It includes SU, S7 and BA. Why not put together the routing which works best for you, sticking to carriers which DL can write onto and then call DL with your proposal? AC AE AF AH AI AM AR AS AT AV AY AZ A3 A5
A9 BA BB BE BP BR BT B2 CE CI CM CS CX CZ
DL DP EI ET FB FI FJ FM FT FV FZ GA GF GK
G3 HA HP HV HX HY IB IC IG JD JJ JL JO JU
J2 KA KC KE KL KM KQ KS KX LA LG LH LJ LO
LP LR LX LY LZ ME MF MH MI MK MN MQ MS MU
NF NG NH NU NZ OA OE OK OM OO OS OU OZ PC
PG PR PS PY PZ QF RJ RO RP SA SB SK SN SQ
SU SV S2 S5 S7 S9 TA TG TM TN TP TU T0 UA
UK UL UP UX U0 VA VC VE VI VJ VN VO VP VS
VT VW WB WF WK WP WS WX WY XK XL XN X5 YM
ZQ ZR ZZ 3M 4C 4M 4O 4Q 5T 7H 8G 9K 9U 9W