Looking at the way “sujet” is used in French and if your text relates more particularly to roundabout-style rides, I think a reasonable case can be made for Charles’ “mounts”.

Presumably the term does refer to “figures” as in the horse or animal figures/models/characters traditionally used in roundabouts and has come now also to include other types of mounts, e.g. vehicles, etc.

See here for “Sujets de manège” for sale
http://www.stockmanege.com/Sujets-occasions-cbhaaaaaa.asp

and a UK auction site for “Fairground - Ride mounts”
http://www.elephanthouseauctions.com/taggedresults.php?t=43

Chaque carrousel dispose de sujets surprenants qui peuvent s’élever dans les airs ou basculer d’avant en arrière
Les chevaux de bois figés laissent place à des sujets mouvants
Si certains manèges d’origine, datant de plusieurs dizaines d’années, ont gardé l’authenticité des chevaux de bois, ou sujets plus traditionnels, d’autres carrousels innovent et proposent des sujets divers et variés :
• Des voitures, camions, bus et autres automobiles,
• Des fusés, avions et autres sujets volants,
• Des personnages de dessins animés,
• Des buggy’s ou petites camionnettes de safari,…
http://www.fete-foraine.be/fr/dir/metier/25/carrousels

Sujets/figures au profit des manèges enfantins et train fantômes
http://www.romyrides.com/index2.aspx?id=2_2&taal=F

He became a major supplier of mounts for roundabouts built by the likes of Savage of King’s Lynn and was regarded by many as the finest showman’s carver of them all.
He produced a huge variety of animal figures for fairground roundabouts, ranging from the usual galloping horses to ostriches, bears lions, donkeys, pigs, goats and turkeys.
…
Within the peak period of twenty years, some 32 similar machines were either built new, rebuilt, or modified by Orton’s, while Spooner concentrated on the various vehicles and other mounts that changed as taste dictated. Once again, he showed great innovation in producing spectacular offerings like dragon cars, whales, Father Neptunes, dolphins and peacocks.
…
Arks came originally from Germany and were so called because of their animal-shaped mounts.
http://fairground-heritage.org.uk/learning/fairground-people...

Until cars came along humankind relied on the horse for transportation and horses have been, perhaps, the most common form of roundabout mount for the past few centuries.
…
The bicycle and horse were not the only things Savage bolted to a roundabout. Using boats was an obvious move and a ride called Sea-on-Land made use of replica ships that were made to rock and pitch on cranks attached to large wheels moving over a circular track beneath a revolving platform.
This idea was also applied to mounts other than boats. The so-called “platform Gallopers” of the early 1880s used this idea, replacing boats with horses – another variant used galloping cockerels.
…
The mounts themselves were exquisitely carved by the leading exponents of the day, men like Spooner and Anderson. And some rides weren’t satisfied just with horses, but mixed them up with cockerels, ostriches, bears, farm animals and hybrid figures that were half horse, half Cavalry officer.
http://fairground-heritage.org.uk/learning/swings-and-rounda...

In 1937 Orton & Spooner countered when they fulfilled an order (Corrigans) for an Ark with motorcycle mounts, a concept exploiting the current popularity of motorcycle speedway racing.
…
Meanwhile, a direct and obvious development of the Noah’s Ark lay in the fitting of movable cars to the platform in place of fixed mounts.
http://fairground-heritage.org.uk/learning/fairground-people...