Paulo,
You will find that there are freezing microtomes out there gathering 
dust but I would go with the suggestions of a portable "cryostat" 
(two or three on the market, I am sure the vendors will soon 
approach you).
 I have used a CO2 freezing microtome many years ago and they 
do produce a good quality section (very rapid freezing) and is fine 
for a one of section (forget serials) albeit a little thick by todays 
standards, but perfectly diagnosable.
If you do get one please be aware of the ferocity of the CO2 jet as 
in inexperienced hands I have seen "splats" of tissue on the inner 
side of the freezing cover and bits of tissue projected across the 
room when the cover is forgotten! (there could also be a safety 
issue here,aerosols etc.).
Terry.
Terry Hacker,
Medical Research Council,
Harwell,
Didcot,
Oxfordshire, OX11 ORD
01235 834393 x360