Saying that there is a conditional multimodal distribution is somewhat like trying to prove a negative. For example, a bimodal distribution is really strong evidence, in most cases, of hidden variable bias. The heights of people is a common bimodal distribution but the hidden variable there is gender.
In other words, for me to say that a distribution is conditionally multimodal would be to affirmatively state that there was not hidden variable that could be the underlying cause.
Do multimodal distributions occur naturally? Yes. Are they conditionally multimodal? Probably not.
For some phenomena to be naturally bimodal (to use the simplest multimodal distribution) would mean that there would have to exist some threshold x where conditional population y behaves differently upon surpassing that threshold.
Even in the above lawyer salary, the hidden variable bias is the firm that hires them. In essence, the conditional distribution is unimodal once firm type is controlled for.
Another example of a multimodal distribution that is only so due to being an unconditional distribution: school district total revenue. Condition on locale (rural, urban, suburban) and you find you have three unimodal distributions.