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I'd like to point out that orienteering maps are generally in the 1:10 000
range, maybe 1:5000, but not to my knowledge 1:1000 or 1:500. This is below
the scale even of town planning  maps, and into the scale of architects'
plans.
 
May I suggest sampling municipal mapping in the 1"=200' (1: 2400) or even
1"=100' (1:1200) range? Some municipalities map in trees in their enginering
maps at this scale, but you'd be hard pressed to find color maps much below
1:10 000. Another place to check is with the campus planners and/or
engineering depts at Universities and such, vegetation often being a major
feature of campuses.
 
The Ordnance Survey maintains maps down to 1:1250 of dense urban centers, but
I don't know how you'd get these.
 
I have a friend who has done very detailed forest-tract GIS surveys (i.e.
every tree above 6" diameter mapped by height, species and diameter, using
GPS to place them), but from what he tells me, this is relatively unusual.
And the printouts he was using were not down to 1:500.