Is there any scriptures which describes about the name, size, weight of their Gada? And how they got them?
As discussed in the answers to this question, contrary to popular belief Hanuman doesn't have a Gada. Hanuman generally fought using trees, rocks, and bare hands. However, this chapter of the Sundara Kanda of the Ramayana describes him finding and using an iron rod briefly:
The glorious Hanuma, having been free from his bonds, again assumed the form equal to a mountain and while looking around, found an iron rod belonging to the arched door-way. That long-armed Hanuma, again taking that rod made of iron, killed all those guards. That Hanuma, having an impetuous valour in combat, destroying those demons and looking over Lanka, shone like the sun encircled with rays, with the wreath of flames blazing on his tail.
Hanuman's brother Bhima, on the other hand, definitely had a Gada. The Mahabharata doesn't mention where he got it, but it does provide a few details about it: it was heavy, eight-sided, made of Saikya iron, and adorned with gold. Here is what this chapter of the Varna Parva of the Mahabharata says:
And Bhimasena, armed with a mace entirely of Saikya iron and embossed with gold, rushed towards the Saindhava monarch doomed to death.
And here is what this chapter of the Udyoga Parva says:
Even now I see that terrible mace of his, with eight sides made of steel, and adorned with gold, uplifted like a Brahmana's curse.