There is no specific parameter for this, how about using a filter?
Like this:
Get-User -Filter "distinguishedName -like 'CN=*,OU=This-one,OU=OU,DC=domain,DC=local'"
Otherwise, get-aduser cmd-let allows you to specify the search scope as follows:
get-aduser -searchbase "OU=This-one,OU=OU,DC=domain,DC=local" -searchscope 1
Link:
http://technet.microsoft.com/en-us/library/ee617241.aspx
Arcass