The spawn locations follows as below:

Astrocetus and Astrodelphis: Extremely rare spawn at Asgard in the Mountains.

Voidwyrm: They spawn in Asgard.

Tropical Wyvern: spawn alongside beaches.

Blood Wyvern: spawn in the West Swamp Isle in Midgard.

Ember Wyvern: spawn rarely in Volcano and Ice Wyvern Trench in Jotunheim.

Sinomacrops: rarely spawns in Red Woods area in Midgard's NE and at some points in Vanaheim.

Dinopithecus: rarely spawn in Midgard's Red Woods area.

Amargasaurus, Fenrir and Managarmr: spawn casually scattered at Jotunheim.

Bloodstarker: spawn rarely as West of Vanaheim and Western Swamp in main map.

Phoenix and X-Phoenix: rarely spawn at Midgard's Volcano.

Reaper and R-Reapers: spawn at Rock Drake's Trench.

Morellatops, Lymantria, Jerboa and Noglin: spawn rarely at Argard mountain areas.

Enforcer, Scout and Tek Stryder: can be craft summoned at random levels (and with random equipments in Stryder case) using the Portable Terminal structure added in the mod (unlockable at level 105). They also spawn in Asgard, Tek Stryder doesn't requires mission to tame.

Tek Variants: 5% chance to replace its Normal or Aberrant counterparts.

Aberrant Variants: spawn between Vanaheim and Argard scattered through the maps.

R-Variants: spawn between Argard (most of all) and Midgard scattered through the map.

X-Variants: X-Volcano spawn in Midgard's Volcano, X-Ocean spawn in West Ocean area in Midgard (where X-Dunkleosteos spawn normally), X-Bog spawn in Vanaheim and X-Snow spawn in Jotunheim.

Europasaurus: spawn in Midgard's grasslands, X in Vanaheim rarely.

Styracosaurus and Stygimoloch: spawn at beach areas.

Rock Elemental (non-X): spawn in Midgard's Volcano area.

Rhyniognatha: Rare spawn in Vanaheim and Western Swamp in main map.

Nameless: SE Aberrant Cave.

Obs: certain creature spawns may be affected by some events, like Tek Trike and Tek Gigas won't spawn properly because of their Skeletal variants in Fear Evolved events, due to how Wild Card handles the events. 😑