If you have the speed and time data, you can use gradient() to get the acceleration.
ts=0.1;
t=0:ts:7;
Speed=sin(t);
Accel=gradient(Speed,ts);
plot(t,Speed,'r',t,Accel,'b');
legend({'Speed','Accel'});
If you want to get it directly in Simulink, use a Derivative block. You might need to consider filtering first to remove noise.
Or do you mean this?
ts=0.5;
t=0:ts:4;
Speed=sin(t);
Accel=gradient(Speed,ts);
dt=gradient(t,ts);
plot(t,Speed);
hold on;quiver(t,Speed,dt,Accel);
