Since the collection does not contains all supported maps so far, I thought it would be useful to make a list, so you know what other maps you can download and expect them to work in gamemode:

• dd_darkest_days
  
• dd_ironisle_v2
  
• dm_outlying_v2
  
• dm_A_lesser_fate
  
• dm_abyss
  
• dm_shockstreet_b2
  
• dm_biohazard
  
• de_nightfever
  
• dm_filth_v1
  
• dm_backbone
  
• dm_torque
  
• dm_astera
  
• dm_datacore
  
• dm_zest
  
• dm_lockdown
  
• dm_7hour
  
• dm_raven
  
• dm_thorn
  
• dm_resistance
  
• dm_damage_inc
  
• dm_energize_b1
  
• dm_hell_night_v1
  
• ts_steel
  
• dm_stad
  
• dm_instant
  
• fy_highrise_09
  
• dm_postoffice
  
• dm_steamlab
  
• dm_sordid_b3
  
• cs_office
  
• fy_forest
  
• dm_phallan
  
• dm_villa_b3
  
• dm_balcony_beta4
  
• dm_plaza17
  
• dm_cloudcity
  
• dm_border_bust
  
• dm_cigaro
  
• dm_megawatt
  
• dm_dust_housing_estate4
  
• fy_garage
  
• dm_derelict_final
  
• dm_detritus_v2
  
• dm_moil_final
  
• dm_hellhole_b94b
  
• dm_facility_beta
  
• dm_rebels_2
  
• dm_avalon
  
• dm_powerhouse
  
• dm_scepter
  
• dm_trainyard
  
• dm_3006_beta1
  
• dm_archt
  
• dm_area22
  
• dm_cannon_r1
  
• dm_casual
  
• dm_closecombat
  
• dm_corrodeb5
  
• dm_fallout
  
• dm_greenhouse
  
• dm_gunshotbeta4
  
• dm_insomnia_v1
  
• dm_laststop
  
• dm_lostarena
  
• dm_loststation
  
• dm_metro
  
• dm_necessity
  
• dm_six
  
• dm_suspended
  
• dm_thefactory
  
• dm_thumper
  
• dm_tobor
  
• dm_tower_arena_v2
  
• dm_transport
  
• dm_underpass
  
• de_nuke
  
• de_inferno
  
• de_train
  
• dm_bridge_b2
  
• dm_amplitude
  
• dm_downtown
  
• dm_graveyard
  
• cs_pariah
  
• dm_overwatch
  
• cs_apartments
  
• fy_skystep
  
• de_industry

Any other map should work too, but they will be limited to Free for All and Team Deathmatch gametypes (Punchpocalypse should work too, I think)

If you need to edit mapcycle, it is located at garrysmod/data/darkestdays/dd_mapcycle.txt