shuriken?

The simple answer is that no, shuriken are not legal for your dad to import.

The FIREARMS AND OFFENSIVE WEAPONS ACT, 1990 (OFFENSIVE WEAPONS) ORDER, 1991 made it an offense to manafacture, import, sell, hire or loan a list of specific offensive weapons.

http://www.irishstatutebook.ie/ZZSI66Y1991.html

Item (i) on that list are shuriken :

( i ) the weapon sometimes known as a shuriken, shaken or death star, being a hard non-flexible plate having three or more sharp radiating points and designed to be thrown;

Were someone to already own Shuriken then Section 9 of Firearms and Offensive Weapons Act would be the relevant legislation covering transporting them etc. With that said, that legislation is intended to apply to adults - workmen, sportspeople and so on.

OFFENSIVE WEAPONS
The importation of Offensive Weapons listed in S.I. No.66 1991 is totally prohibited. [Firearms and
Offensive Weapons Act, 1990 (No. 12 of 1990) and the Firearms and Offensive Weapons Act, 1990
(Offensive Weapons) Order, 1991 (S.I. No. 66 of 1991)]. For the purposes of this prohibition the term
“offensive weapons” means:
(a) a flick knife, that is to say -
(i) a knife which opens when hand pressure is applied to a button, spring, lever or other device in
or attached to the handle, or
(ii) a knife which has a blade which is released from the handle or sheath by the force of gravity
or the application of centrifugal force and when released is locked in an open position by
means of a button, spring, lever or other device;
(b) a knuckleduster, that is to say -
(i) a band of metal or other hard material worn on one or more fingers, and designed to cause
injury, or
(ii) any weapon incorporating a knuckleduster;
(c) a swordstick or dagger cane, that is, a hollow walking-stick or cane containing a blade which
may be used as a sword or dagger;
(d) a sword umbrella, that is an umbrella containing a blade which may be used as a sword;
(e) any weapon from which one or more sharp spikes protrude which is worn attached to the
foot, ankle, hand or wrist (sometimes known when intended to be attached to the foot, as a
footclaw and, when intended to be attached to the hand, as a handclaw);
(f) the weapon sometimes known as a belt buckle knife, being a buckle which incorporates or
conceals a knife;
(g) the weapon sometimes known as a push dagger, being a knife the handle of which fits within a
clenched fist and the blade of which protrudes from between two fingers;
(h) the weapon sometimes known as a hollow kubotan, being a cylindrical container containing a
number of sharp spikes;
(i) the weapon sometimes known as a shuriken, shaken or death star, being a hard non-flexible
plate having three or more sharp radiating points, and designed to be thrown;
(j) the weapon sometimes known as a balisong or butterfly knife, being a blade enclosed by its
handle, which is designed to split down the middle, without the operation of a spring or other
mechanical means, to reveal the blade;
(k) the weapon sometimes known as a telescopic truncheon or telescopic billy, being a truncheon
which extends automatically by hand pressure applied to a button, spring or other device in or
attached to its handle;
(l) the weapon sometimes known as a blowpipe or blow gun, being a hollow tube out of which hard
pellets or darts are shot by the use of human breath;
(m) the weapon sometimes known as a kusari gama, being a length of rope, cord wire or chain
fastened at one end to a sickle;
(n) the weapon sometimes known as a kyoketsu shoge, being a length of rope, cord, wire or chain
fastened at one end to a hooked knife;
(o) the weapon sometimes known as a manrikigusari or kusari being a length or rope, cord, wire or
chain fastened at each end to a hard weight or hand grip;
(p) the weapon sometimes known as a sap glove, being a glove into which metal or some other hard
material has been inserted or to which metal or such material has been attached;
(q) the broad knife known as a machete or matchet.

what a crock