Can give a couple of personal recommendations
(1) If just looking for a good supplier, worth the short trip up to Torrevieja to Garcia Brothers (Hnos Garcia) who have 3 massive outlets there all in fairly close proximity to each other - near Carrefour if you're familiar with the area. You'll see these recommended on various Forums
(2) If you're looking for someone to effectively project manage everything eg supply, install and do the fiddly bits like curtain rails etc, could try local company called 'Golf & Beach Properties' who I've used previously. Director Markus Brall lives in Los Alcacarez and I know they work area Murcia up to Alicante. Don't have his local info to hand but can try email info@golfandbeachproperties.co.uk. Ideal for say UK-based landlords etc and much cheaper than you may imagine.
I have no affiliation to either of above but am happy to vouch for either.. Hope this helps