I think you have to work at it a bit.

Don't have to be 'aggressive' or bid high to take it from others but farming is a long term deal and you will have to tell others you would like the opportunity to farm their land is they are ever looking for a tenant or new tenant 

Sometimes it can take many years before operator of a parcel changes and then your reputation and operation will help you get the extra land.

I have had people I know that stopped in as I 'matured' just to tell me if I ever wanted to rent my land they were interested or if I needed custom work done they were interested in the business too.

Although I was not renting then it was no fault of theirs that I rented some to next door neighbour (they do some custom work for that neighbour) and I did not consider his approach to be anything more than letting me know he was interested.