Casio-Basic, 125 bytes

For 1⇒a To n:For 1⇒b To n:For 1⇒c To n:If((s*(s-a)*(s-b)*(s-c))|s=(a+b+c)/2)=n^2:Then:Print{a,b,c}:Stop:IfEnd:Next:Next:Next

Turns out you can use : to string commands into a single line!

Standard brute force solution. 124 bytes for the code, 1 byte to specify n as a parameter.

Casio Basic, 123 bytes

For 1⇒a To n 
For 1⇒b To n 
For 1⇒c To n 
If(s*(s-a)*(s-b)*(s-c)|s=(a+b+c)/2)=n^2 
Then 
Print{a,b,c} 
Stop 
IfEnd 
Next:Next:Next

Standard brute force solution. 122 bytes for the code, 1 byte to specify n as a parameter.