In our parish and diocese, there most certainly are programs/retreats/prayer groups for single Catholics as well as widows/widowers.  We have programs for seniors and youth.  We even have programs for parents of LGBT children.  

I would hazard a guess that MOST parishes and dioceses have similar programs.

In addition, there is no reason in the world that the unmarried/widowed could not attend any and all programs not specifically geared to married persons.