I'm having some trouble finding values for the horizontal reactions. All help is appriciated.
Once you know the vertical reactions you can analise each of the pin joints in turn. For example at point C the vertical reaction is 18.75 but we know that the total reaction must be in the direction of C-D (otherwise the beam would rotate around its pin joints).
If we want the force to be directed down 4 units for every 5 horizontal force units then we need 5 units of force for every 4 units of horizontal force. That is 18.75 * 5 / 4 = 23.44.
A similar argument applies at B only here the ratio is 2.5/4.
The horizonta force at A can then be found by recognising that the sum of the horizontal forces must be zero (as the beam is not moving).