Random Deterministic Automata
The question is a bit ill-posed, since you did not specify that equivalent automata should be counted as a single object. Without that restriction (or the reachability one), the set of all $n$-state DFAs over a binary alphabet and with starting state $s=1$ has exactly $n^{2n}2^n$ elements, and it is trivial to sample from this set uniformly, as indicated in the link in my comment,
https://dl.acm.org/citation.cfm?id=3064434

Now the linked paper gives sharp bounds on the expected size of the minimal equivalent DFA, when the original one is drawn from the naive uniform distribution. For binary alphabets, this quantity is concentrated about $0.7968n$. That suggests that if you naively sample DFAs on $n/0.7968$ states and then minimize them, you'll get automata with roughly $n$ reachable states. Of course, no claim is being made about this sampling procedure being uniform. See, however, references in the linked paper -- especially
https://dl.acm.org/citation.cfm?id=782472
and
http://www.sciencedirect.com/science/article/pii/S0304397507002861?via%3Dihub
-- the latter seems most relevant to your question.