The split of the sales commission between the two reps should be the same as the resale properties. For instance, if the commission paid by the developer is 4% and you bring a replacement buyer, you should get 2.5% of the commission while the rep in the lineup (think of them as the listing rep) will get 1.5%. Make sure you get each rep you work with to agree to these numbers in writing via email, preferably before the broker event.
Alternatively, you may want to wait for the 10 cooling off period after the broker sales event to expire so that these units gets returned to the developer, not to the sales reps whose buyers bailed, allowing you to sell it and gather a full commission rather than split it with another rep. In any case, after the broker event make sure you find out exactly what units are getting returned (get unit #s) plus their selling price from any of the sales reps that have the best positions in the lineup.
Also, be sure to contact the developer or exclusive broker during the 10 day cooling off period and tell them you want the opportunity to be a deal salvager. Ask them how much time they will give you to sell these remaining units at the same price they were bought and returned for and if you will be paid the same commission as at the broker event. If (at the broker event) there was a limit on the number of units each broker could sell plus a limit on how many units each client could buy, ask them if they’re flexible on those limitations since you are not (technically speaking) selling units during the broker event, merely mopping up and salvaging deals that would otherwise be lost.