Could sodium azide be produced from the reaction of urea and sodium nitrate or nitrite
CH4N2O + NaNO3 = NaN3 + 2 H2O + CO2
or
CH4N2O + NaNO2 = NaN3 + 2 H2O + CO
Or is this reaction just impossible?
Yes if you add some hydrazine salt like NH2-NH3HSO4 or NH2-NH3Cl and that you neutralize afterwards...but then urea is useless.
Alternatively if you have a positive chlorine reactant you could make N,N'-dichloro-urea and allow this to react with excess NH3...then with NaNO2 to
yield some NaN3.
All those processes passes via hydrazine intermediaries...