Making the Specular map separate in a shader (not as alpha)?

I'm not good with shaders.

Can someone tell me how I would take the skin shader below (from the wiki) and make the specular map be a separate texture instead of getting it from the alpha of the MainTex?

I'm loading textures from the user's hard drive and since Unity can't load a DDS or anything with an actual alpha channel (unless I use an asset pack but user's can't make those) I need to use a separate texture as the spec map.

Thanks in advance!

Shader "Skin/Bumped Specular" {
Properties {
    _Color ("Main Color", Color) = (1,1,1,1)
    _SpecColor ("Specular Color", Color) = (0.5, 0.5, 0.5, 1)
    _Shininess ("Shininess", Range (0.01, 1)) = 0.078125
    _MainTex ("Base (RGB) Gloss (A)", 2D) = "white" {}
    _BumpMap ("Bump (RGB)", 2D) = "white" {}
    _RimTex ("Rim ramp (GRB) Fresnel ramp (A)", 2D) = " grey" {}
    _WrapTex ("Wrap ramp (RGBA)", 2D) = "grey" {}

// ------------------------------------------------------------------
// Fragment program

SubShader {
    Blend AppSrcAdd AppDstAdd
    Fog { Color [_AddFog] }
    TexCount 4

    UsePass  "Skin/Specular/BASE"

    // Pixel lights
    Pass {
        Name "PPL"
        Tags { "LightMode" = "Pixel" }
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile_builtin
#pragma fragmentoption ARB_fog_exp2
#pragma fragmentoption ARB_precision_hint_fastest 
#include "UnityCG.cginc"
#include "AutoLight.cginc" 
#include "skinhelpers.cginc"
struct v2f {
    float3  uvK;    // xy = UV, z = specular K
    float3  viewDirT;
    float3  lightDirT;
    float2  bumpUV;

uniform float _Shininess;
uniform float4 _MainTex_ST, _BumpMap_ST;

v2f vert (appdata_tan v)
    v2f o;
    PositionFog( v.vertex, o.pos, o.fog );
    o.uvK.z = _Shininess * 128;
    o.uvK.xy = TRANSFORM_TEX(v.texcoord, _MainTex);
    o.bumpUV = TRANSFORM_TEX(v.texcoord, _BumpMap);

    o.lightDirT = normalize (mul (rotation, ObjSpaceLightDir( v.vertex )));
    o.viewDirT = normalize (mul (rotation, ObjSpaceViewDir( v.vertex )));

    return o;

uniform sampler2D _MainTex;
uniform sampler2D _BumpMap;

float4 frag (v2f i)  : COLOR
    half4 texcol = tex2D( _MainTex, i.uvK.xy );
    float3 normalT = normalize (tex2D (_BumpMap, i.bumpUV).rgb * 2 - 1);
    return SpecularLightWrap(i.lightDirT, i.viewDirT, normalT, texcol, i.uvK.z, LIGHT_ATTENUATION(i));


Fallback "Skin/Specular", 0 

Not sure how to fix your shader (sorry about that), but unity can load TGA files at editor time and runtime easily enough, and they have a separate alpha channel

Unity can load graphics at runtime (which I assume is what you're talking about) with alpha channels from any format as long as you can code/find an importer for it.