The IMX disappeared from the US market when the GLX was released. However, since Shimano bought Loomis and discountinued the selling of GLX blanks, select models of the IMX blanks has been brought back into production for sale as blanks only. The IMX is still a very nice blank which I have no problem recommending to folks who are looking for a fast, progressive, smooth action rod. The GLX is just noticeably better, although much more costly.
You might be better served by the 9' 6 wt instead of the 5 wt though because it is better able to handle long casts and fish over 4 pounds.